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 A124714 #12 Apr 30 2025 14:00:01
%S A124714 1,21,61,141,377,1001,2737,7553,21073,59217,167441,475793,1357637,
%T A124714 3887541,11165509,32152901,92802433,268398401,777651553,2256800033,
%U A124714 6558953917,19087539437,55614451789,162219429293,473648632141
%N A124714 Number of base 21 circular n-digit numbers with adjacent digits differing by 1 or less.
%C A124714 [Empirical] a(base,n)=a(base-1,n)+A002426(n+1) for base>=1.int(n/2)+1
%C A124714 a(n) = T(n, 21) 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,..,21}. See theorem 3.3 in Knopfmacher and others, reference in A124696. - _Peter Luschny_, Aug 13 2012
%H A124714 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 A124714 (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 A124714 nonn,base
%O A124714 0,2
%A A124714 _R. H. Hardin_, Dec 28 2006