This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A189536 #16 Jan 25 2025 03:12:56
%S A189536 0,2,3,5,17,37,101,0,401,3137,4357,62501,21317,16901,1008017,15877,
%T A189536 1020101,33857,69697,14401,331777,78401,32401,57601,828101,40195601,
%U A189536 32080897,3326977,876097,476101,199374401,4326401,14440001,1299601,33918977,3459601,2647719937,145540097
%N A189536 The smallest prime p such that tau(p-1) + tau(p+1) = prime(n), or 0 if no such prime exists; where tau(k) is the number of divisors of k.
%C A189536 This is sequence A090482(n) for prime n.
%t A189536 nn = 25; t = Table[-1, {nn}]; t[[1]] = 0; t[[8]] = 0; cnt = 2; p = 1; While[cnt < nn, p = NextPrime[p]; s = DivisorSigma[0, p - 1] + DivisorSigma[0, p + 1]; If[PrimeQ[s], i = PrimePi[s]; If[i <= nn && t[[i]] == -1, t[[i]] = p; cnt++]]]; t (* _T. D. Noe_, Apr 28 2011 *)
%Y A189536 Cf. A000005, A000668, A002496, A090482, A175144 (tau(p-1)+tau(p+1)).
%K A189536 nonn
%O A189536 1,2
%A A189536 _Juri-Stepan Gerasimov_, Apr 23 2011
%E A189536 a(26)-a(38) from _Amiram Eldar_, Jan 25 2025