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 A240597 #36 Feb 09 2021 01:57:08 %S A240597 1,15,24,42,60,64,69,78,90,100,114,123,133,147,153,177,186,198,222, %T A240597 231,240,258,259,270,276,288,289,306,339,360,366,393,402,403,414,429, %U A240597 438,447,459,474,477,492,495,501,507,511,522,582,588,594,600 %N A240597 Numbers k such that sigma(k) == k (mod 9). %C A240597 That is, numbers k that satisfy the following: %C A240597 A010878(k) = A105852(k) or A010878(k) = A010878(A000203(k)). %C A240597 A010888(k) = A190998(k) or A010888(k) = A010888(A000203(k)). %H A240597 Ivan N. Ianakiev, <a href="/A240597/b240597.txt">Table of n, a(n) for n = 1..10000</a> %F A240597 A010888(a(n)) = A010888(A000203(a(n))). %F A240597 A010888(a(n)) = A190998(a(n)). %e A240597 sigma(15) = 24. 24 == 15 (mod 9), therefore 15 is in the sequence. %t A240597 Select[Range[1000],Mod[#,9]==Mod[DivisorSigma[1,#],9]&] %Y A240597 Cf. A000203, A190998, A010878, A105852, A010888. %K A240597 easy,nonn %O A240597 1,2 %A A240597 _Ivan N. Ianakiev_, Sep 13 2014