A085378 Difference between primes p and the largest prime divisor of p-1.

3, 4, 6, 10, 15, 16, 12, 22, 26, 34, 36, 36, 24, 40, 30, 56, 56, 64, 70, 66, 42, 78, 94, 96, 86, 54, 106, 106, 120, 118, 120, 116, 112, 146, 144, 160, 84, 130, 90, 176, 172, 190, 190, 188, 204, 186, 114, 210, 204, 222, 236, 246, 255, 132, 202, 266, 254, 274, 236

Offset: 3

Author

Cino Hilliard, Aug 12 2003

Keywords

• easy
• nonn

Comments

This sequence contains only one prime number, the 3.

Examples

			For prime 107 we have 107 - 53 = 54.
		

Programs

Maple

A085378 := proc(n)
    ithprime(n)-A023503(n) ;
end proc:
seq( A085378(n),n=3..80) ; # R. J. Mathar, Sep 07 2016

Mathematica

#-FactorInteger[#-1][[-1,1]]&/@Prime[Range[3,70]] (* Harvey P. Dale, Jan 04 2012 *)

PARI

cminuspm1(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); ) ) }