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 A227991 #17 Sep 08 2022 08:46:05
%S A227991 3,1,3,1,3,1,9,1,3,3,1,1,3,1,3,27,3,1,1,9,1,1,3,9,1,3,1,27,1,3,1,3,3,
%T A227991 1,3,1,1,1,3,3,9,1,3,1,9,1,1,1,3,1,9,3,1,9,3,3,27,1,1,3,1,3,1,3,1,3,1,
%U A227991 1,3,1,3,9,1,1,1,3,3,1,3,1,3,1,27,1,1,3,9
%N A227991 Highest power of 3 dividing prime(n)+1.
%H A227991 Bruno Berselli, <a href="/A227991/b227991.txt">Table of n, a(n) for n = 1..1000</a>
%F A227991 a(n) = 3^A227990(n).
%t A227991 Table[3^IntegerExponent[Prime[n] + 1, 3], {n, 100}]
%o A227991 (PARI) forprime(p=2, 700, print1(3^valuation(p+1, 3), ", "));
%o A227991 (Magma) [3^Valuation(NthPrime(n)+1, 3): n in [1..100]];
%Y A227991 Cf. A068503 (highest power of 3 dividing prime(n)-1), A068504 (highest power of 2 dividing prime(n)+1), A227990.
%K A227991 nonn
%O A227991 1,1
%A A227991 _Bruno Berselli_, Aug 05 2013