A056139 a(n) = n^2 - primefloor(n)*primeceiling(n).

0, 0, 1, 0, 1, 0, -13, 4, 23, 0, 1, 0, -25, 4, 35, 0, 1, 0, -37, 4, 47, 0, -91, -42, 9, 62, 117, 0, 1, 0, -123, -58, 9, 78, 149, 0, -73, 4, 83, 0, 1, 0, -85, 4, 95, 0, -187, -90, 9, 110, 213, 0, -211, -102, 9, 122, 237, 0, 1, 0, -243, -118, 9, 138, 269, 0, -133, 4, 143, 0, 1, 0, -291, -142, 9, 162, 317, 0, -157, 4, 167, 0, -331, -162, 9

Offset: 2

Author

Henry Bottomley, Jun 15 2000

Keywords

• easy
• sign

Comments

a(n)= 0 iff n is prime.

Examples

			a(3)=3^2-3*3=0, a(4)=4^2-3*5=1
		

Links

• Antti Karttunen, Table of n, a(n) for n = 2..65537

Crossrefs

Cf. A007917, A007918, A030664, A056140, A056141.

Programs

PARI

A030664(n) = if (n < 2, 1, precprime(n)*nextprime(n)); \\ From A030664
A056139(n) = (n^2 - A030664(n)); \\ Antti Karttunen, Mar 20 2018

Formula

a(n) = n^2 - A007917(n)*A007918(n) = A000290(n) - A030664(n).

Extensions

More terms from Antti Karttunen, Mar 20 2018