Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #38 Jul 15 2022 08:06:57
%S 7,79,47,113,130783,523927,1198297,240641,641,575058377,1519711993,
%T 65929327,20105355479017,9007199254738183,7633399,33189241,
%U 21081993227096629777,951850902549409,4978773308244222679,501615233613780359,9671406556917033397642519,8251206137,3818597055399121,13314319257913,521211122055087383048446607
%N a(n) is the largest prime factor of 2^p - p^2 where p is the n-th prime.
%C All prime factors of 2^p - p^2 are congruent to 1 or 7 (mod 8). (See A001132.) - _Robert G. Wilson v_, Mar 14 2022
%D E.-B. Escott, Note #1642, L'Intermédiaire des Mathématiciens, 8 (1901), page 12.
%H Amiram Eldar, <a href="/A350964/b350964.txt">Table of n, a(n) for n = 3..95</a>
%H Robert G. Wilson v, <a href="/A350964/a350964_2.txt">Factorization of 2^p - p^2 for n = 3..120</a>
%F a(n) = A006530(A098105(n)). - _Amiram Eldar_, Mar 03 2022
%p a:= n-> max(numtheory[factorset]((p-> 2^p-p^2)(ithprime(n)))):
%p seq(a(n), n=3..27); # _Alois P. Heinz_, Mar 03 2022
%t a[n_] := FactorInteger[2^(p = Prime[n]) - p^2][[-1, 1]]; Array[a, 25, 3] (* _Amiram Eldar_, Mar 03 2022 *)
%o (PARI) a(n) = my(p=prime(n)); vecmax(factor(2^p - p^2)[,1]); \\ _Michel Marcus_, Mar 03 2022
%Y Cf. A001132, A006530, A072180, A098105, A117587.
%K nonn
%O 3,1
%A _N. J. A. Sloane_, Mar 02 2022