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 A247954 #26 Jul 10 2025 19:39:35
%S A247954 1,7,12,15,14,28,24,60,39,42,63,60,32,90,72,63,124,124,60,120,96,84,
%T A247954 168,124,80,195,120,195,186,168,96,210,224,126,252,195,114,224,252,
%U A247954 186,133,224,280,360,234,248,255,360,171,392,216,210,508,280,216,300
%N A247954 a(n) = sigma(sigma(2n-1)).
%C A247954 See A247821 - numbers k such that sigma(sigma(2k-1)) is a prime p.
%H A247954 Indranil Ghosh, <a href="/A247954/b247954.txt">Table of n, a(n) for n = 1..10000</a>
%F A247954 a(n) = A000203(A000203(2n-1)) = A000203(A008438(n-1)) = A051027(2n-1).
%e A247954 For n=2; a(2) = sigma(sigma(2*2-1)) = sigma(sigma(3)) = sigma(4) = 7.
%p A247954 with(numtheory): A247954:=n->sigma(sigma(2*n-1)): seq(A247954(n), n=1..50); # _Wesley Ivan Hurt_, Oct 01 2014
%t A247954 Table[DivisorSigma[1, DivisorSigma[1, 2 n - 1]], {n, 50}] (* _Wesley Ivan Hurt_, Oct 01 2014 *)
%o A247954 (Magma) [SumOfDivisors(SumOfDivisors(2*n-1)): n in [1..1000]];
%o A247954 (PARI) vector(100,n,sigma(sigma(2*n-1))) \\ _Derek Orr_, Sep 29 2014
%Y A247954 Cf. A000203, A051027, A008438, A247820.
%K A247954 nonn,easy
%O A247954 1,2
%A A247954 _Jaroslav Krizek_, Sep 28 2014