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 A124851 #18 Apr 30 2025 14:34:54
%S A124851 1,9,39,141,587,2479,10731,47063,208547,931047,4180239,18849103,
%T A124851 85269011,386687375,1756855951,7993210831,36405316227,165940691695,
%U A124851 756832203759,3453347063599,15762537566627,71964915505967
%N A124851 Number of base 9 circular n-digit numbers with adjacent digits differing by 2 or less.
%C A124851 [Empirical] a(base,n)=a(base-1,n)+A005191(n+1) for base>=2.int(n/2)+1.
%C A124851 See A285280 for confirmation of linear recurrence and code to produce sequence; also confirms conjectured g.f. from _Colin Barker_. - _Ray Chandler_, Aug 12 2023.
%H A124851 Ray Chandler, <a href="/A124851/b124851.txt">Table of n, a(n) for n = 0..99</a>
%H A124851 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>
%H A124851 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (9, -21, -7, 50, -4, -30, 4, 4).
%F A124851 G.f.: (1 - 21*x^2 - 14*x^3 + 150*x^4 - 16*x^5 - 150*x^6 + 24*x^7 + 28*x^8) / ((1 + x)*(1 - 4*x + 2*x^2)*(1 - 6*x + 5*x^2 + 8*x^3 - 4*x^4 - 2*x^5)). - _Colin Barker_, Jun 02 2017
%o A124851 (S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-1](($[i]`-$[(i+1)mod N]`>2)+($[(i+1)mod N]`-$[i]`>2))
%Y A124851 Cf. Row 9 of A285280.
%K A124851 nonn,base
%O A124851 0,2
%A A124851 _R. H. Hardin_, Dec 28 2006