

A240234


Least number k such that k*n^k + 1 is prime, or 0 if no such number exists.


3



1, 1, 2, 1, 1242, 1, 34, 5, 2, 1, 10, 1
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OFFSET

1,3


COMMENTS

a(n) = 1 if and only if n + 1 is prime.
Next term a(13), if it exists, is greater than 1000000. Other unknown terms are at index: 25, 29, 41, 47, 49, 53, 55, 69, 73, 79. (See links).  Jeppe Stig Nielsen, Aug 08 2014


LINKS

Table of n, a(n) for n=1..12.
Guenter Loeh, Generalized Cullen primes n b^n + 1
Jeppe Stig Nielsen, Table of a(n) for n = 1..100, with unknown entries denoted by question marks


EXAMPLE

1*3^1 + 1 = 4 is not prime. 2*3^2 + 1 = 19 is prime. Thus, a(3) = 2.


PROG

(PARI) a(n) = for(k=1, 4000, if(ispseudoprime(k*n^k+1), return(k)))
n=1; while(n<100, print1(a(n), ", "); n++)


CROSSREFS

Cf. A089001, A116954.
Sequence in context: A272538 A087037 A036109 * A098940 A098939 A180215
Adjacent sequences: A240231 A240232 A240233 * A240235 A240236 A240237


KEYWORD

nonn,hard,more


AUTHOR

Derek Orr, Apr 02 2014


STATUS

approved



