A102926 Smallest prime factor in product of previous terms +1 or -1.
2, 3, 5, 29, 11, 7, 13, 37, 17, 79, 23, 4129, 193, 2593, 101, 19, 39163, 577, 26431, 131, 308798542881428667318174028327605372989, 103, 163, 179, 293, 127, 6287, 683437, 31, 89, 13590243019242466336587034391, 113, 2207, 59, 109, 223, 2351
Offset: 1
Keywords
Examples
a(5)=11 because 2*3*5*29=870, 869=11*79, 871=13*67. a(31) = 13590243019242466336587034391 because this is the least prime factor of A102927(30)+1. The least prime factor of A102927(30)-1 is 44989026625856465412069667987. Remarkably, both are 29-digit numbers. - _David Wasserman_, Apr 15 2008
Links
- Donovan Johnson, Table of n, a(n) for n = 1..111
Programs
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Mathematica
spf[{p_,a_}]:=With[{f=FactorInteger[p^2-1][[1,1]]},{p*f,f}]; NestList[ spf,{2,2},36][[All,2]] (* Harvey P. Dale, May 05 2018 *)
Formula
a(n) = least prime factor of b(n)^2-1, where b(n) = product a(k), 0A102927.
Extensions
More terms from Don Reble, Jan 23 2005, corrected Sep 26 2006
Further terms from David Wasserman, Apr 15 2008
Comments