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 A097349 Numbers n such that (Sum (2k)^k, k=1..n) + 1 is prime. 1
 1, 2, 13, 72, 318, 13583 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Some of the larger entries may only correspond to probable primes. The numbers produced by 72 and 318 have now been certified prime by Primo. 13583, found by PrimeForm using recurrence mode, corresponds to a 60228-digit probable prime. - Rick L. Shepherd, Apr 29 2006 LINKS EXAMPLE 13 is a term as 2^1 + 4^2 + 6^3 + 8^4 + 10^5 + 12^6 + 14^7 + 16^8 + 18^9 + 20^10 + 22^11 + 24^12 + 26^13 + 1 = 2518267981703965963, which is prime (certified with Primo). PROG (PARI) s=1; for(k=1, 700, s=s+(2*k)^k; if(isprime(s), print1(k, ", "))) CROSSREFS Cf. A073825 (Sum k^k, k=1..n, is prime), A097350 ((Sum (2k)^k, k=1..n) - 1 is prime). Sequence in context: A264735 A289926 A188676 * A289790 A109112 A163190 Adjacent sequences:  A097346 A097347 A097348 * A097350 A097351 A097352 KEYWORD more,nonn AUTHOR Rick L. Shepherd, Aug 07 2004 EXTENSIONS One more term from Rick L. Shepherd, Apr 29 2006 STATUS approved

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Last modified May 23 07:08 EDT 2019. Contains 323508 sequences. (Running on oeis4.)