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A097350 revision #4

A097350

Numbers n such that (Sum (2k)^k, k=1..n) - 1 is prime.

2, 3, 6, 49

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OFFSET

1,1

COMMENTS

Some of the larger entries may only correspond to probable primes.

Term 49 corresponds to a certified prime (Primo 2.2.0 beta). Next term is greater than 5400. - Ryan Propper (rpropper(AT)stanford.edu), Aug 23 2005

LINKS

Table of n, a(n) for n=1..4.

EXAMPLE

6 is a term as 2^1 + 4^2 + 6^3 + 8^4 + 10^5 + 12^6 - 1 = 3090313, which is prime.

PROG

(PARI) s=-1; for(k=1, 830, s=s+(2*k)^k; if(isprime(s), print1(k, ", ")))

CROSSREFS

Cf. A073825 (Sum k^k, k=1..n, is prime), A097349 ((Sum (2k)^k, k=1..n) + 1 is prime).

Sequence in context: A049383 A099411 A018372 * A323721 A277374 A062309

Adjacent sequences: A097347 A097348 A097349 * A097351 A097352 A097353

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Aug 07 2004

STATUS

approved