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A100605 Numbers k such that (prime(k)-1)! + prime(k)^2 is prime. 2
1, 2, 4, 10, 26 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

k = {1, 2, 4, 10, 26} yields primes p(k) = {2, 3, 7, 29, 101}. There are no more such k up to k=100. Verified by Ray Chandler.

a(6) > 750. - Jinyuan Wang, Apr 10 2020

LINKS

Table of n, a(n) for n=1..5.

FORMULA

Numbers k such that (prime(k)-1)! + prime(k)^2 is prime, where prime(k) is the k-th prime.

EXAMPLE

a(3) = 4 because (prime(4)-1)! + prime(4)^2 = (7-1)! + 7^2 = 720 + 49 = 769 is prime and is the 3rd such prime of that form.

PROG

(PARI) is(k) = ispseudoprime((prime(k)-1)! + prime(k)^2); \\ Jinyuan Wang, Apr 10 2020

CROSSREFS

Cf. A100604, A100858.

Sequence in context: A085633 A111564 A007021 * A247395 A183947 A154322

Adjacent sequences:  A100602 A100603 A100604 * A100606 A100607 A100608

KEYWORD

nonn,hard,more

AUTHOR

Jonathan Vos Post, Nov 30 2004

STATUS

approved

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Last modified June 25 03:09 EDT 2021. Contains 345449 sequences. (Running on oeis4.)