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A126018
Smallest prime of the form 1 + Sum{j=1..n} k^(2*j-1).
0
2, 3, 43, 5, 683, 7, 10101010101011, 43691, 174763, 11, 2796203, 13, 1074532291189456211731158116986854092943409, 10518179715343122711873674826619717982095485405484801996888751
OFFSET
1,1
COMMENTS
Primes arising in A124151.
If n=(prime number-1) then a(n) = prime(n). - Artur Jasinski, Dec 23 2006
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
KEYWORD
nonn
AUTHOR
Artur Jasinski, Dec 14 2006
EXTENSIONS
Edited and extended by Klaus Brockhaus, Dec 16 2006
STATUS
approved