A014981 a(n) = c(prime(n))/prime(n), where c = Perrin sequence A001608 (starting 0,2,3,...) and prime(n) is the n-th prime.

1, 1, 1, 1, 2, 3, 7, 11, 28, 120, 197, 892, 2479, 4148, 11687, 56010, 271913, 461529, 2270882, 6599404, 11263855, 56250108, 164879269, 830987861, 7231032935, 21386730355, 36802336319, 109099442316, 187943217386

Offset: 1

Author

Clark Kimberling, Robert G. Wilson v

Keywords

• nonn
• easy
• nice

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..1000 (terms 1..200 from T. D. Noe)
• Ondrej Such, An Insufficient Condition for Primality, Problem 10268, Amer. Math. Monthly, Vol. 103, No. 10 (1996), p. 911.

Crossrefs

See A001608, the main entry for the Perrin sequence.

Cf. A000040, A052338, A064723.

Programs

PARI

c(n) = polsym(x^3-x-1,n)[n+1]; \\ A001608
a(n) = my(p=prime(n)); c(p)/p; \\ Michel Marcus, Mar 03 2022