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A320468
a(n) = a(n-1) + 20*a(n-2), n >= 2; a(0)=1, a(1)=41.
2
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
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
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Aug 27 2019
STATUS
approved