A117101 Numbers k such that nextprime(5*k) > 5*nextprime(k) and k is composite.

18, 28, 40, 60, 72, 78, 82, 96, 102, 105, 106, 155, 156, 166, 178, 180, 192, 222, 226, 228, 250, 262, 266, 267, 268, 270, 280, 282, 292, 312, 328, 329, 330, 334, 335, 336, 352, 358, 378, 387, 388, 396, 408, 418, 420, 436, 437, 438, 460, 485, 486, 490, 496, 497

Offset: 1

Author

Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Apr 18 2006

Keywords

• easy
• nonn

Links

• Paolo Xausa, Table of n, a(n) for n = 1..10000

Crossrefs

Set difference of A117094 and A000040.

Intersection of A002808 and A117094.

Cf. A007918 (nextprime).

Programs

Mathematica

Select[Range[500], CompositeQ[#] && NextPrime[5*#] > 5*NextPrime[#] &] (* Paolo Xausa, Jul 28 2025 *)

PARI

for(i=1,300,if(nextprime(5*i)>nextprime(5)*nextprime(i) && !isprime(i),print1(i,",")))

Extensions

Name simplified by Paolo Xausa, Jul 28 2025