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Old 2020-02-23, 16:20   #1
enzocreti
 
Mar 2018

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Default Primes of the form 30*n^2-1

Because I found that the prime 5879 is in some mysterious way involved in pg primes
And realizing that 5879 is a prime of the form 30*n^2-1, I wonder if in oesi there is a sequence of primes of this form
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Old 2020-02-23, 17:14   #2
carpetpool
 
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Nov 2016

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You could always make one yourself if it doesn't exist:

Code:
(09:13) gp > g=[]; for(i=1,300, if(isprime(30*i^2-1), g=concat(g,i)))
(09:13) gp > g
%5 = [1, 3, 4, 10, 14, 17, 18, 21, 22, 25, 29, 34, 35, 38, 42, 43, 48, 52, 55, 56, 60, 62, 63, 67, 73, 74, 78, 80, 90, 92, 94, 95, 99, 101, 105, 108, 113, 116, 118, 119, 126, 127, 129, 130, 132, 133, 139, 140, 143, 147, 153, 154, 157, 178, 181, 183, 186, 190, 192, 195, 199, 200, 207, 213, 216, 221, 224, 225, 232, 234, 238, 242, 244, 248, 251, 256, 259, 265, 269, 273, 276, 281, 284, 288, 290, 294, 297, 300]
(09:13) gp >
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Old 2020-02-24, 04:17   #3
CRGreathouse
 
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For a more general approach:
Code:
polyToSeqPrimes(p)=my(v=List(),len,x=variable(p),n,t); while(len<=260, if(isprime(t=subst(p,x,n)), listput(v,t); len+=#Str(t)+2); n++); v=Vec(v); v[1..#v-1];
polyToSeqIndices(p)=my(v=List(),len,x=variable(p),n); while(len<=260, if(isprime(subst(p,x,n)), listput(v,n); len+=#Str(n)+2); n++); v=Vec(v); v[1..#v-1];
polyToPrimeBFile(p)=my(v=vector(10^4),x=variable(p),n,i,t); while(i<#v, if(isprime(t=subst(p,x,n)), v[i++]=t); n++); v;
polyToIndexBFile(p)=my(v=vector(10^4),x=variable(p),n,i); while(i<#v, if(isprime(subst(p,x,n)), v[i++]=n); n++); v;

polyToSeqPrimes(30*'n^2-1)
polyToSeqIndices(30*'n^2-1)
Just enter the polynomial desired and get the primes and their indices computed for you. (Versions for 10,000 term b-files included as well.)
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Old 2020-02-25, 10:47   #4
enzocreti
 
Mar 2018

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Quote:
Originally Posted by carpetpool View Post
You could always make one yourself if it doesn't exist:

Code:
(09:13) gp > g=[]; for(i=1,300, if(isprime(30*i^2-1), g=concat(g,i)))
(09:13) gp > g
%5 = [1, 3, 4, 10, 14, 17, 18, 21, 22, 25, 29, 34, 35, 38, 42, 43, 48, 52, 55, 56, 60, 62, 63, 67, 73, 74, 78, 80, 90, 92, 94, 95, 99, 101, 105, 108, 113, 116, 118, 119, 126, 127, 129, 130, 132, 133, 139, 140, 143, 147, 153, 154, 157, 178, 181, 183, 186, 190, 192, 195, 199, 200, 207, 213, 216, 221, 224, 225, 232, 234, 238, 242, 244, 248, 251, 256, 259, 265, 269, 273, 276, 281, 284, 288, 290, 294, 297, 300]
(09:13) gp >



I note that there are pairs (21,22) (42,43) (126,127) with 21,42,126 multiple of 7


Is it unlikely that these consecutive (a,b) are infinitely many?
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Old 2020-02-25, 10:51   #5
enzocreti
 
Mar 2018

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Quote:
Originally Posted by carpetpool View Post
You could always make one yourself if it doesn't exist:

Code:
(09:13) gp > g=[]; for(i=1,300, if(isprime(30*i^2-1), g=concat(g,i)))
(09:13) gp > g
%5 = [1, 3, 4, 10, 14, 17, 18, 21, 22, 25, 29, 34, 35, 38, 42, 43, 48, 52, 55, 56, 60, 62, 63, 67, 73, 74, 78, 80, 90, 92, 94, 95, 99, 101, 105, 108, 113, 116, 118, 119, 126, 127, 129, 130, 132, 133, 139, 140, 143, 147, 153, 154, 157, 178, 181, 183, 186, 190, 192, 195, 199, 200, 207, 213, 216, 221, 224, 225, 232, 234, 238, 242, 244, 248, 251, 256, 259, 265, 269, 273, 276, 281, 284, 288, 290, 294, 297, 300]
(09:13) gp >



I note that there are pairs (21,22) (42,43) (126,127) (62,63)...(a,b) with either a or b multiple of 7...do you believe these pairs with consecutive a,b are infinite?




I call a(n) the n-th term of the sequence


so it seems that there are infinitely many terms a(n) such that a(n+1)=a(n)+1


a(n)=21 a(n+1)=23=a(n)+1

Last fiddled with by enzocreti on 2020-02-25 at 11:15
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Old 2020-03-01, 02:10   #6
carpetpool
 
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"Sam"
Nov 2016

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Quote:
Originally Posted by enzocreti View Post
I note that there are pairs (21,22) (42,43) (126,127) with 21,42,126 multiple of 7


Is it unlikely that these consecutive (a,b) are infinitely many?


We cannot prove or disprove this at the moment, but it should be implied there exist infinitely many pairs by one of Dickinson's conjecture. The pattern continues:

(18:08) gp > g=[]; for(i=1,2000, if(isprime(30*i^2-1) & isprime(30*i^2+60*i+29) & i%7==0, g=concat(g,[[i,i+1]])))
(18:09) gp > g
%12 = [[21, 22], [42, 43], [126, 127], [224, 225], [399, 400], [455, 456], [469, 470], [686, 687], [693, 694], [742, 743], [777, 778], [833, 834], [1057, 1058], [1092, 1093], [1127, 1128], [1309, 1310], [1484, 1485], [1659, 1660], [1673, 1674], [1750, 1751], [1792, 1793], [1806, 1807]]
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