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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified April 3 19:43 EDT 2020. Contains 333198 sequences. (Running on oeis4.)