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 2019-04-16, 22:11 #6 Pietro Maiorana   Feb 2019 3 Posts (Start) A100319+1 (Even numbers m such that at least one of m-1 and m+1 is composite) can be obtained as the union of: 3*A005818; 5*A038179 without 2; 7*A007310 without 1; A038511 A025584 without 2, 3. (End) ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ The sequence A038511 can be obtained by multiplying each term of A008364 , except {1}, by itself and by all subsequent terms. Rewrite the terms in ascending order. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ (Start) To obtain A025584 (Primes p such that p-2 is not a prime): Write all terms of the form 2k + 7 and delete all terms of the form (6k + (-1) ^ k + 13)/2 [without A121764] and all terms of A092256 Finally, add 2 and 3. (End) To calculate A121764 (Single, or isolated or non-twin primes of form 6n + 1) consider all term of A092256(n) + 2 except those in common with: A038511, 5*A038179, and 7*A007310. A092256 (Nonprimes of form 6k+5) is the union of: numbers of the form 5*(6k + 1) , numbers of the form 7*(6k + 5), and terms of A038511 of the form 3*k+2 ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Last fiddled with by Pietro Maiorana on 2019-04-16 at 22:15