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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 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 January 21 10:05 EST 2022. Contains 350476 sequences. (Running on oeis4.)