Project Description

[Joe O]

This project is an extension of the original Sierpinski/Riesel problems. It is attempting to solve the Sierpinski/Riesel problems for base 5 by determining the smallest Sierpinski/Riesel base 5 numbers. Therefore, primes of the form k*5^n+/-1 are being sought for even k's.

A distributed effort is currently ongoing in support of the project.

Sierpinski Base 5 - The smallest even k Sierpinski base 5 number is suggested to be k=159986. To prove this, it is sufficient to show that k*5^n+1 is prime for each even k < 159986. This has currently been achieved for all even k, with the exception of the following 47 values:
k = 6436, 7528, 10918, 24032, 26798, 29914, 31712, 36412, 37292, 41738, 44348, 44738, 45748, 51208, 55154, 58642, 59912, 60394, 62698, 64258, 67612, 67748, 68492, 71492, 74632, 76724, 77072, 81556, 83936, 84284, 90056, 92158, 92182, 92906, 93484, 105464, 109208, 109988, 110488, 118568, 126134, 133778, 138514, 139196, 144052, 152588, 154222

Riesel Base 5 - The smallest even k Riesel base 5 number is suggested to be k=346802. To prove this, it is sufficient to show that k*5^n-1 is prime for each even k < 346802. This has currently been achieved for all even k, with the exception of the following 130 values
k = 1396, 2488, 3622, 4906, 5374, 11812, 17152, 18656, 22478, 22934, 23906, 26222, 27994, 35248, 35816, 48764, 49568, 52922, 53546, 57406, 63838, 64598, 66916, 68132, 70082, 71146, 72532, 76354, 81134, 84466, 88444, 92936, 97366, 97768, 100186, 102818, 102952, 102976, 104944, 109238, 109838, 109862, 114986, 119878, 127174, 130484, 131848, 134266, 136804, 138172, 143632, 145462, 145484, 146264, 146756, 147844, 150344, 151042, 152428, 154844, 159388, 162434, 162668, 164852, 170386, 170908, 171362, 173198, 174344, 175124, 177742, 178658, 180062, 182398, 187916, 189766, 190334, 194368, 195872, 201778, 204394, 206894, 207394, 207494, 210092, 213988, 231674, 238694, 239062, 239342, 243686, 243944, 245114, 246238, 248546, 256612, 259072, 262172, 265702, 266206, 267298, 268514, 270748, 271162, 273662, 285598, 285728, 289184, 296024, 298442, 301016, 301562, 304004, 305716, 306398, 313126, 316594, 318278, 322498, 325918, 325922, 326834, 327926, 329584, 330286, 331882, 335414, 338866, 338948, 340168

History
Robert Smith originally presented the idea of a Sierpinski/Riesel base 5 search on 2004-9-17, in the primeform yahoo group. Using {3,7,13,31,601} as the covering set, he proposed that k=346802 is the smallest Riesel base 5 number. Shortly afterwards, Guido Smetrijns proposed that k=159986 is the smallest Sierpinski base 5 number.
After doing most of the initial work himself, Robert posted in the mersenneforum.org on 2004-9-28, and thus, the distributed effort began. Other principle players in the development, management, and growth of the project are Lars Dausch, Geoff Reynolds, Anand S Nair, and Thomas Masser.

Primes Reported
As of 2011-01-02 there have been 352 primes reported in this forum, 1 of them this year: S/R Base 5 Primes in 2011


There were 33 primes reported in 2010. S/R Base 5 Primes in 2010
There were no primes reported in 2009.
There were 10 primes reported in 2008.
There were 31 primes reported in 2007.
There were 126 primes reported in 2006.
There were 129 primes reported in 2005.
There were 22 primes reported in 2004, the starting year of this project.

[Aillas]

Not up to date. If you have time:

It seems it's now 45 SB5 & 117 RB5.
Stat for 2011 too?

Thanks.

[Dead J. Dona]

2013 primes

[Joe O]

Originally Posted by Aillas

Stat for 2011 too?

Thanks.

S/R Base 5 Primes in 2011

S/R Base 5 Primes in 2012

2013 see post just above this one

S/R Base 5 Primes in 2014

S/R Base 5 Primes in 2015

S/R Base 5 Primes in 2016

[sweety439]

Now there are:

30 Sierpinski k's remain (at n=3.3M): {6436, 7528, 10918, 26798, 29914, 31712, 36412, 41738, 44348, 44738, 45748, 51208, 58642, 60394, 62698, 64258, 67612, 67748, 71492, 74632, 76724, 83936, 84284, 90056, 92906, 93484, 105464, 126134, 139196, 152588}

62 Riesel k's remain (at n=3.3M): {3622, 4906, 23906, 26222, 35248, 52922, 63838, 64598, 68132, 71146, 76354, 81134, 92936, 102818, 102952, 109238, 109862, 127174, 131848, 134266, 136804, 143632, 145462, 145484, 146756, 147844, 151042, 152428, 154844, 159388, 164852, 170386, 170908, 177742, 182398, 187916, 189766, 190334, 195872, 201778, 204394, 206894, 213988, 231674, 239062, 239342, 246238, 248546, 259072, 265702, 267298, 271162, 273662, 285598, 285728, 298442, 304004, 313126, 318278, 325922, 335414, 338866}

See http://primegrid.com/stats_sr5_llr.php for the large primes, also see http://www.primegrid.com/forum_thread.php?id=5087

[kar_bon]

A new prime for the Riesel side was found:

102818 *5^3440382-1 is prime.

There're still values in progress for this k by PrimGrid, so the Wiki-page will list it, too.

There's also a page for the Sierpiński-side.