A239666 a(n) = least number k such that n*k^n+1 is prime, or 0 if no such number exists.

1, 1, 4, 1, 8, 1, 4, 3, 10, 1, 42, 1, 60, 15, 22, 1, 8, 1, 198, 42, 10, 1, 8, 115, 34, 21, 0, 1, 54, 1, 130, 3, 4, 7, 72, 1, 778, 204, 30, 1, 108, 1, 178, 15, 14, 1, 924, 28, 234, 63, 1376, 1, 44, 3, 16, 27, 256, 1, 180, 1, 706, 51, 98, 0, 546, 1, 4, 153, 150, 1, 170

Offset

1,3

Comments

a(n) = 1 iff n+1 is prime.

If a(n) = 0, then n is in A097792. Note that the converse is not true: a(4) = 1, not 0.

Links

Table of n, a(n) for n=1..71.

Example

3*1^3+1 = 4 is not prime. 3*2^3+1 = 25 is not prime. 3*3^3+1 = 82 is not prime. 3*4^3+1 = 193 is prime. Thus, a(3) = 4.

Prog

(PARI) Pf(n) = for(k=1, 10^4, if(ispseudoprime(n*k^n+1), return(k))); n=1; while(n<50, print(Pf(n)); n+=1)

Crossrefs

Cf. A097792, A116954, A089001.

Sequence in context: A143320 A089146 A297402 * A101512 A085994 A179836

Adjacent sequences: A239663 A239664 A239665 * A239667 A239668 A239669

Keyword

nonn

Author

Derek Orr, Mar 29 2014

Status

approved