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 A061904 #3 Oct 27 2023 22:00:46 %S A061904 1,3,6,9,10,12,15,18,21,30,39,45,48,51,60,90,100,102,105,111,120,150, %T A061904 180,201,210,249,300,318,321,348,351,390,450,480,501,510,549,600,900, %U A061904 1000,1002,1005,1011,1020,1050,1101,1110,1149,1200,1500,1761,1800,2001 %N A061904 Numbers n such that the iterative cycle: n -> sum of digits of n^2 has only one distinct element. %C A061904 Since the only numbers invariant under this iteration are 1 and 9, n is contained in this sequence iff the sum of digits of n^2 is 1 or 9. %e A061904 6 -> 3+6 = 9 -> 8+1 = 9 thus 9 is the only element of the iterative cycle of 6. 12 -> 1+4+4 = 9 -> 8+1 = 9 ... %Y A061904 Cf. A007953, A004159, A061903 - A061910. %K A061904 nonn,base %O A061904 1,2 %A A061904 _Asher Auel_, May 17 2001