A085382 Sum of p = prime(n) and largest prime divisor of p-1.

5, 7, 10, 16, 16, 19, 22, 34, 36, 36, 40, 46, 50, 70, 66, 88, 66, 78, 78, 76, 92, 124, 100, 100, 106, 120, 160, 112, 120, 134, 144, 154, 162, 186, 156, 170, 166, 250, 216, 268, 186, 210, 196, 204, 210, 218, 260, 340, 248, 262, 256, 246, 256, 259, 394, 336, 276, 300

Offset: 2

Author

Cino Hilliard, Aug 12 2003

Keywords

• easy
• nonn

Examples

			a(2) = prime(2) + gpf(prime(2) - 1) = 3 + gpf(2) = 3 + 2 = 5.
		

Crossrefs

Cf. A006530, A023503, A274022.

Programs

PARI

cminuspm2(n) = \\ prime + maxprime of prime-1
{ forprime(x=5,n, forstep(p=x,2,-1, if(isprime(p) & (x-1)%p==0,print1(x+p,","); break); ) ) }

PARI

a(n) = my(p=prime(n)); p+vecmax(factor(p-1)[,1]); \\ Michel Marcus, May 07 2024

Formula

a(n) = p + A006530(p-1) where p = prime(n).

Extensions

Offset 2 and a(2) from Michel Marcus, May 07 2024

Edited by Jon E. Schoenfield, May 07 2024