A289357 Least number k such that n^2 + n - k is prime.

0, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 5, 1, 11, 1, 1, 13, 5, 1, 1, 1, 3, 5, 1, 3, 1, 5, 1, 7, 1, 1, 5, 5, 3, 1, 5, 7, 1, 1, 3, 1, 5, 3, 1, 1, 1, 5, 1, 3, 1, 5, 3, 1, 1, 1, 1, 5, 9, 1, 1, 3, 17, 5, 1, 1, 1, 7, 1, 13, 1, 5, 19, 3, 19, 7, 1, 19, 11, 3, 7, 5, 3, 1, 11, 1

Offset

1,7

Comments

a(A045546(n)) = 1.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = A049711(A002378(n)). - Robert Israel, Jul 03 2017

Maple

0, seq(n^2 + n - prevprime(n^2+n), n=2..100); # Robert Israel, Jul 03 2017

Mathematica

Table[k = 0; While[! PrimeQ[n^2 + n - k], k++]; k, {n, 85}] (* Michael De Vlieger, Jul 04 2017 *)

Prog

(PARI) for(n=1, 85, k={my(k=0); while(!isprime(n^2+n-k), k++); k; }; print1(k", "))

Crossrefs

Cf. A002378, A045546, A049711, A161550 (resulting primes).

Sequence in context: A131324 A371884 A079724 * A111368 A140750 A028264

Adjacent sequences: A289354 A289355 A289356 * A289358 A289359 A289360

Keyword

nonn

Author

Gionata Neri, Jul 03 2017

Status

approved