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 A131418 #12 May 10 2019 08:35:23 %S A131418 0,9,18,27,36,45,54,63,72,81,108,117,126,135,144,153,162,171,207,216, %T A131418 225,234,243,252,261,279,306,315,324,333,342,351,369,378,405,414,423, %U A131418 432,441,459,468,477,504,513,522,531,549,558,567,576,603,612,621,639 %N A131418 Numbers n such that Sum_digits(n)=Sum_digits[n+Sum_digits(n)], with n>=0. %C A131418 Conjecture: all terms are divisible by 9. - _Harvey P. Dale_, Mar 28 2019 %e A131418 n=315 --> 3+1+5=9 --> 315+9=324 --> 3+2+4=9. %e A131418 n=873 --> 8+7+3=18 --> 873+18=891 --> 8+9+1=18. %p A131418 P:=proc(n) local a,i,k,w; for i from 0 by 1 to n do w:=0; k:=i; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; a:=w; k:=i+w; w:=0; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; if a=w then print(i); fi; od; end: P(1000); %t A131418 Select[Range[0,700],Total[IntegerDigits[#]]==Total[IntegerDigits[#+ Total[ IntegerDigits[ #]]]]&] (* _Harvey P. Dale_, Mar 28 2019 *) %o A131418 (PARI) isok(n) = my(sn = sumdigits(n)); sn == sumdigits(n+sn); \\ _Michel Marcus_, May 10 2019 %Y A131418 Cf. A007953, A131417. %K A131418 easy,nonn,base %O A131418 1,2 %A A131418 _Paolo P. Lava_ and _Giorgio Balzarotti_, Jul 09 2007