A126018 - OEIS

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A126018

Smallest prime of the form 1 + Sum{j=1..n} k^(2*j-1).

2, 3, 43, 5, 683, 7, 10101010101011, 43691, 174763, 11, 2796203, 13, 1074532291189456211731158116986854092943409, 10518179715343122711873674826619717982095485405484801996888751

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OFFSET

1,1

COMMENTS

Primes arising in A124151.

If n=(prime number-1) then a(n) = prime(n). - Artur Jasinski, Dec 23 2006

LINKS

Table of n, a(n) for n=1..14.

EXAMPLE

Consider n = 8. 1 + Sum{j=1...8} k^(2*j-1) evaluates to 9 for k = 1 and to 43691 for k = 2. 9 is composite but 43691 is prime, hence a(8) = 1+2+2^3+2^5+2^7+2^9+2^11+2^13+2^15 = 43691.

PROG

(PARI) {for(n=1, 14, k=1; while(!isprime(s=1+sum(j=1, n, k^(2*j-1))), k++); print1(s, ", "))} - Klaus Brockhaus, Dec 16 2006

CROSSREFS

Cf. A006093, A124151, A124205-A124209, A124164, A124178, A124181, A124185-A124187, A124189, A124200, A124154, A124163.

Sequence in context: A334533 A196874 A087571 * A257467 A255092 A237414

Adjacent sequences: A126015 A126016 A126017 * A126019 A126020 A126021

KEYWORD

nonn

AUTHOR

Artur Jasinski, Dec 14 2006

EXTENSIONS

Edited and extended by Klaus Brockhaus, Dec 16 2006

STATUS

approved