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 A256307 #5 Oct 09 2023 18:48:07
%S A256307 1,2,3,4,5,6,0,21,22,23,24,25,26,20,31,32,33,34,35,36,30,41,42,43,44,
%T A256307 45,46,40,51,52,53,54,55,56,50,61,62,63,64,65,66,60,1,2,3,4,5,6,0,211,
%U A256307 212,213,214,215,216,210,221,222,223,224
%N A256307 Apply the transformation 0 -> 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 0 to the digits of n written in base 7; do not convert back to base 10.
%C A256307 Base 7 variant of A256078 (base 2) and A048379 (base 10). See A256303 - A256308 for bases 3 through 8, A256289 for base 9, and A256297 for the variant where the result is converted back to base 10.
%e A256307 a(7) = 21 because 7 = "10" (in base 7) becomes "21".
%e A256307 a(48) = 0 because 48 = "66" (in base 7) becomes "00".
%t A256307 Table[FromDigits[IntegerDigits[n,7]/.{0->1,1->2,2->3,3->4,4->5,5->6,6->0}],{n,0,60}] (* _Harvey P. Dale_, Oct 09 2023 *)
%o A256307 (PARI) A256307(n,b=7)=!n+eval(Strchr(apply(d->(d+1)%b+48, digits(n,b))))
%K A256307 nonn,base,easy
%O A256307 0,2
%A A256307 _M. F. Hasler_, Mar 22 2015