A126488 Number of base 20 n-digit numbers with adjacent digits differing by three or less.

1, 20, 128, 840, 5560, 36988, 246840, 1650808, 11056590, 74130748, 497387482, 3339002940, 22423219250, 150623072388, 1011962290858, 6799752144942, 45694220498130, 307084056184964, 2063824981953422, 13870824556736138

Offset

0,2

Comments

[Empirical] a(base,n)=a(base-1,n)+7^(n-1) for base>=3n-2; a(base,n)=a(base-1,n)+7^(n-1)-2 when base=3n-3.

Links

Table of n, a(n) for n=0..19.

Formula

G.f.: (1+9*x-69*x^2-55*x^3+242*x^4+192*x^5-94*x^6-73*x^7+5*x^8+4*x^9) / (1-11*x+23*x^2+53*x^3-82*x^4-100*x^5+30*x^6+35*x^7-x^8-2*x^9) (conjectured). - Colin Barker, Jul 18 2017

Prog

(S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-2](($[i]`-$[i+1]`>3)+($[i+1]`-$[i]`>3))

Crossrefs

Cf. Base 20 differing by two or less A126407, one or less A126374.

Sequence in context: A219710 A263229 A125330 * A304507 A005551 A006417

Adjacent sequences: A126485 A126486 A126487 * A126489 A126490 A126491

Keyword

nonn,base

Author

R. H. Hardin, Dec 27 2006

Status

approved