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 A196225 #24 Jan 22 2025 00:08:57
%S A196225 1,0,2,4,0,16,6,64,0,0,0,12,36,4096,24,0,0,48,0,262144,0,0,0,144,0,0,
%T A196225 0,60,0,268435456,120,576,0,0,0,3072,0,68719476736,180,900,0,240,0,
%U A196225 4398046511104,0,0,0,5184,0,0,0,0,0,196608,0,960,46656,0,0,360,0,1152921504606846976
%N A196225 Smallest number k such that sigma(tau(k)) = n, or 0 if there is no such k.
%C A196225 Smallest number k such that A062069(k) = A000203(A000005(k)) = n, or 0 if there is no such k.
%H A196225 Amiram Eldar, <a href="/A196225/b196225.txt">Table of n, a(n) for n = 1..3323</a>
%H A196225 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts#Inversion_of_Multiplicative_Functions">PARI/GP Scripts for Miscellaneous Math Problems: Inversion of Multiplicative Functions</a> (invphi.gp).
%F A196225 a(n) = 0 iff A051444(n) = 0.
%e A196225 a(6) = 16 because number 16 is the smallest number k such that sigma(tau(k)) = 6; (tau(16) = 5, sigma(5) = 6).
%o A196225 (PARI) a(n) = {my(v = invsigma(n), kmin = 0); for(i = 1, #v, k = A005179(v[i]); if(kmin == 0 || k < kmin, kmin = k)); kmin;} \\ _Amiram Eldar_, Jan 21 2025, using _Max Alekseyev_'s invphi.gp and _R. J. Mathar_'s A005179(n)
%Y A196225 Cf. A062069 (sigma(tau(n))), A000203(sigma(n)), A000005(tau(n)), A005179, A051444.
%K A196225 nonn
%O A196225 1,3
%A A196225 _Jaroslav Krizek_, Jan 02 2013
%E A196225 a(24) and a(48) corrected by _Amiram Eldar_, Jan 21 2025