A331698 a(n) = (1/2) * ((greatest prime < (n+1)^2) - (least prime > n^2)) for n >= 2.

1, 1, 3, 1, 5, 4, 6, 7, 6, 6, 9, 10, 13, 12, 13, 12, 14, 15, 19, 18, 18, 15, 21, 21, 25, 20, 26, 17, 23, 27, 28, 31, 30, 31, 35, 33, 32, 37, 34, 33, 35, 36, 34, 43, 39, 42, 45, 33, 45, 45, 48, 45, 53, 42, 46, 55, 49, 51, 56, 53, 60, 52, 60, 60, 63, 64, 61, 53

Offset: 2

Author

Hugo Pfoertner, Jan 27 2020

Keywords

• nonn

Examples

			a(2) = 1 because 7 is the greatest prime < 3^2 and 5 is the least prime > 2^2. (7-5)/2 = 1.
		

Links

• Hugo Pfoertner, Table of n, a(n) for n = 2..10000

Crossrefs

Cf. A007491, A053001, A132657.

Programs

PARI

for(n=2, 69, print1((precprime((n+1)^2)-nextprime(n^2))/2, ", "))