A075296 Interprimes (A024675) which are of the form s*prime, s=21.

42, 105, 231, 399, 483, 861, 987, 1113, 1281, 1491, 1869, 2121, 2247, 2667, 2751, 3129, 3423, 5649, 5691, 5817, 7539, 8169, 8421, 8589, 9807, 10563, 10689, 10983, 11361, 13881, 14511, 14889, 15519, 17031, 17409, 18627, 19761, 20391, 21189

Offset: 1

Author

Zak Seidov, Sep 12 2002

Keywords

• easy
• nonn

Comments

Interprimes of the form s*prime are in A075277-A075296 ( s = 2 - 21 ). Case s=1 is impossible.

Examples

			231 is an interprime and 231/21 = 11 is prime.
		

Links

• David A. Corneth, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A024675, A075277-A075296.

Programs

Mathematica

s=21; Select[Table[(Prime[n+1]+Prime[n])/2, {n, 2, 14000}], PrimeQ[ #/s]&]

PARI

first(n, {m=21}) = {my(res = List(), p); forprime(p=2, oo, if(precprime(m*p) + nextprime(m*p) == 2*m*p, listput(res, m*p); if(#res>=n,return(res))))} \\ David A. Corneth, Jul 26 2017