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 A047903 #16 Feb 19 2024 01:54:48 %S A047903 13,52,364,4732,75712,1665664,56632576,2265303040,56632576000, %T A047903 2265303040000,56632576000000,2265303040000000,56632576000000000, %U A047903 2265303040000000000,56632576000000000000,2265303040000000000000 %N A047903 a(1) = 13; for n > 0, a(n+1) = a(n) * sum of digits of a(n). %C A047903 After the 7th element, every second element has the same beginning. a(9+2k) = 40 * a(8+2k) = 40 * 25 * a(7+2k). %t A047903 NestList[# Total[IntegerDigits[#]]&,13,20] (* _Harvey P. Dale_, Jan 08 2019 *) %Y A047903 Cf. A047892. %K A047903 easy,nonn,base %O A047903 1,1 %A A047903 Miklos SZABO (mike(AT)ludens.elte.hu)