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 A124713 #12 Apr 30 2025 13:59:41
%S A124713 1,20,58,134,358,950,2596,7160,19966,56078,158488,450140,1283848,
%T A124713 3674600,10549282,30365294,87605806,253263470,733498744,2127803180,
%U A124713 6181574548,17982188708,52373316262,152706201170,445700295760
%N A124713 Number of base 20 circular n-digit numbers with adjacent digits differing by 1 or less.
%C A124713 [Empirical] a(base,n)=a(base-1,n)+A002426(n+1) for base>=1.int(n/2)+1
%C A124713 a(n) = T(n, 20) where T(n, k) = Sum_{j=1..k} (1+2*cos(j*Pi/(k+1)))^n. These are the number of smooth cyclic words of length n over the alphabet {1,2,..,20}. See theorem 3.3 in Knopfmacher and others, reference in A124696. - _Peter Luschny_, Aug 13 2012
%H A124713 OEIS Wiki, <a href="/wiki/Number_of_base_k_circular_n-digit_numbers_with_adjacent_digits_differing_by_d_or_less">Number of base k circular n-digit numbers with adjacent digits differing by d or less</a>
%o A124713 (S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-1](($[i]`-$[(i+1)mod N]`>1)+($[(i+1)mod N]`-$[i]`>1))
%K A124713 nonn,base
%O A124713 0,2
%A A124713 _R. H. Hardin_, Dec 28 2006