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 A124712 #13 Apr 30 2025 13:59:22
%S A124712 1,19,55,127,339,899,2455,6767,18859,52939,149535,424487,1210059,
%T A124712 3461659,9933055,28577687,82409179,238128539,689345935,1998806327,
%U A124712 5804195179,16876837979,49132180735,143192973047,417751959379
%N A124712 Number of base 19 circular n-digit numbers with adjacent digits differing by 1 or less.
%C A124712 [Empirical] a(base,n)=a(base-1,n)+A002426(n+1) for base>=1.int(n/2)+1
%C A124712 a(n) = T(n, 19) 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,..,19}. See theorem 3.3 in Knopfmacher and others, reference in A124696. - _Peter Luschny_, Aug 13 2012
%H A124712 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 A124712 (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 A124712 nonn,base
%O A124712 0,2
%A A124712 _R. H. Hardin_, Dec 28 2006