A056141 a(n) = primefloor(n)*primeceiling(n) - previousprime(n)*nextprime(n).

-1, 0, 4, 0, -6, 0, 0, 0, 30, 0, -18, 0, 0, 0, 42, 0, -30, 0, 0, 0, -22, 0, 0, 0, 0, 0, 128, 0, -112, 0, 0, 0, 0, 0, 98, 0, 0, 0, 90, 0, -78, 0, 0, 0, -70, 0, 0, 0, 0, 0, 36, 0, 0, 0, 0, 0, 248, 0, -232, 0, 0, 0, 0, 0, 158, 0, 0, 0, 150, 0, -280, 0, 0, 0, 0, 0, 182

Offset: 3

Author

Henry Bottomley, Jun 15 2000

Keywords

• easy
• sign

Examples

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

Crossrefs

Cf. A056139, A056140.

Cf. A056221 (nonzero terms).

Programs

PARI

a(n) = if (isprime(n), n^2 - precprime(n-1)*nextprime(n+1), 0); \\ Michel Marcus, Mar 22 2020

Formula

a(n) = A007917(n)*A007918(n) - A007917(n-1)*A007918(n+1).

a(n) = A030664(n) - A013638(n).

a(n) = A056140(n) - A056139(n).

a(n) = A056140(n) if n is prime, a(n)=0 otherwise.

Extensions

More terms from Michel Marcus, Mar 22 2020