A320468 a(n) = a(n-1) + 20*a(n-2), n >= 2; a(0)=1, a(1)=41.

1, 41, 61, 881, 2101, 19721, 61741, 456161, 1690981, 10814201, 44633821, 260917841, 1153594261, 6371951081, 29443836301, 156882857921, 745759583941, 3883416742361, 18798608421181, 96466943268401, 472439111692021, 2401777977060041, 11850560210900461, 59886119752101281, 296897323970110501

Offset

0,2

Links

Table of n, a(n) for n=0..24.

Index entries for linear recurrences with constant coefficients, signature (1,20).

Formula

a(n) = (-4)^(n+1) + 5^(n+1).

G.f.: (1+40*x)/((1-5*x)*(1+4*x)).

a(n) == 9*A053428(n)*A224473(n) mod 10^n.

a(n)*A224473(n) == 9*A053428(n) mod 10^n.

Prog

(PARI) {a(n) = (-4)^(n+1)+5^(n+1)}
(PARI) N=40; x='x+O('x^N); Vec((1+40*x)/((1-5*x)*(1+4*x)))

Crossrefs

Cf. A053428, A224473 (trimorphic number), A320469, A321133.

Sequence in context: A031415 A325072 A089345 * A055110 A245317 A039524

Adjacent sequences: A320465 A320466 A320467 * A320469 A320470 A320471

Keyword

nonn,easy

Author

Seiichi Manyama, Aug 27 2019

Status

approved