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 A341621 #13 Apr 01 2024 02:39:54
%S A341621 -1,-1,2,-1,2,1,3,-1,1,1,3,0,3,2,1,-1,4,0,4,0,1,2,4,0,2,2,1,1,4,0,5,
%T A341621 -1,1,3,1,0,5,3,1,0,5,0,5,1,1,3,5,0,2,1,1,1,5,0,2,0,1,3,5,0,5,4,1,-1,
%U A341621 2,0,6,2,1,0,6,0,6,4,1,2,2,0,6,0,1,4,6,0,2,4,1,0,6,0,2,2,1,4,2,0,6,1,1,0,6,0,6,0,1
%N A341621 a(n) is the exponent of the least power of 2 that when multiplied by n makes the product abundant, or -1 if n itself is a power of 2.
%C A341621 Number of iterations of x -> 2x needed before the result is abundant (sigma(x) > 2x), when starting from x=n, or -1 if an abundant number would never be reached (when n is a power of 2).
%H A341621 Antti Karttunen, <a href="/A341621/b341621.txt">Table of n, a(n) for n = 1..65537</a>
%t A341621 a[n_] := Module[{e = IntegerExponent[n, 2], s}, If[n == 2^e, -1, s = DivisorSigma[-1, n/2^e]; Max[Floor[Log2[s/(s - 1)]] - e, 0]]]; Array[a, 100] (* _Amiram Eldar_, Apr 01 2024 *)
%o A341621 (PARI) A341621(n) = if(!bitand(n,n-1), -1, for(i=0,oo,my(n2 = n+n); if(sigma(n) > n2, return(i)); n = n2));
%Y A341621 Cf. A005101 (positions of zeros), A341622 (positions where this differs from A336915).
%K A341621 sign
%O A341621 1,3
%A A341621 _Antti Karttunen_, Feb 19 2021