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A305738 Numbers k such that k!*T(k) - 1 is prime, where T(k) is the k-th triangular number. 1
2, 4, 28, 34, 47, 62, 228, 256, 258, 341, 848, 1362, 1709, 2262, 2692, 7907, 10396, 10501 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The PFGW program has been used to certify all the terms up to a(18), using a deterministic test which exploits the factorization of a(n) + 1. - Giovanni Resta, Jun 24 2018

LINKS

Table of n, a(n) for n=1..18.

Maheswara Rao Valluri, Primes of the form p = 1 + n! Sum n, for some n ∈ N*, arXiv:1803.11461 [math.GM], 2018.

MATHEMATICA

Do[If[ PrimeQ[n(n +1)!/2 - 1], Print@ n], {n, 3000}]

PROG

(PARI) isok(n) = ispseudoprime(n(n+1)!/ 2 - 1);

CROSSREFS

Cf. A302859, A301373.

Sequence in context: A059719 A264930 A226347 * A323447 A227303 A066228

Adjacent sequences:  A305735 A305736 A305737 * A305739 A305740 A305741

KEYWORD

nonn,more

AUTHOR

Maheswara Rao Valluri, Jun 22 2018

EXTENSIONS

a(16)-a(18) from Giovanni Resta, Jun 24 2018

STATUS

approved

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Last modified March 5 16:55 EST 2021. Contains 341827 sequences. (Running on oeis4.)