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 A084054 #8 Aug 21 2014 14:46:20 %S A084054 1,1,2,2,3,3,4,4,0,0,1,1,2,2,3,3,4,4,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, %T A084054 1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3, %U A084054 3,3,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,0,0,0,0,0,0,0 %N A084054 5*n digit-reversed mod 5. %C A084054 The pattern of increasing frequency of repetition of digits is clear. %F A084054 Contribution from _Enrique Pérez Herrero_, Jun 14 2010: (Start) %F A084054 a(n)=mod(floor(5*n/10^(floor(log_10(5*n)))),5), this formula comes from the modulus 5 of the first digit of 5*n. %F A084054 a(10^n)=1 %F A084054 (End) %e A084054 a(61) =3 as, 61*5 = 305,digit reversed = 503 ==3 (mod 5) %t A084054 Contribution from _Enrique Pérez Herrero_, Jun 14 2010: (Start) %t A084054 A084054[n_Integer]:=Mod[FromDigits[Reverse[IntegerDigits[5*n]]],5]; %t A084054 (* Alternative formula *) %t A084054 A084054[n_Integer]:=Mod[Floor[5*n/10^Floor[Log[10,5*n]]],5] (End) %Y A084054 Cf. A084052, A084053, A084055, A084339, A084340, A084341. %K A084054 base,easy,nonn %O A084054 2,3 %A A084054 _Amarnath Murthy_ and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 26 2003 %E A084054 More terms from _Ray Chandler_, May 27 2003