A195118 Numbers with largest and smallest prime factors differing by 6.

55, 91, 187, 247, 275, 385, 391, 605, 637, 667, 1001, 1147, 1183, 1375, 1591, 1925, 1927, 2057, 2431, 2491, 2695, 3025, 3127, 3179, 3211, 4087, 4199, 4235, 4459, 4693, 4891, 5767, 6647, 6655, 6875, 7007, 7387, 7429, 8281, 8993, 9625, 9991, 10807, 11011

Offset: 1

Author

Reinhard Zumkeller, Sep 13 2011

Keywords

• nonn

Examples

			a(10) = 667 = 23 * 29;
a(11) = 1001 = 7 * 11 * 13;
a(12) = 1147 = 31 * 37;
a(13) = 1183 = 7 * 13^2.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..250
• Eric Weisstein's World of Mathematics, Sexy Primes. [The definition in this webpage is unsatisfactory, because it defines a "sexy prime" as a pair of primes.- _N. J. A. Sloane_, Mar 07 2021]

Crossrefs

Cf. A195106, A111192; A143205 is a subsequence.

Programs

Haskell

a195118 n = a195118_list !! (n-1)
a195118_list = filter f [3,5..] where
   f x = last pfs - head pfs == 6 where pfs = a027748_row x

Mathematica

spf6Q[n_]:=With[{fi=FactorInteger[n]},fi[[-1,1]]-fi[[1,1]]==6]; Select[Range[12000],spf6Q] (* Harvey P. Dale, May 14 2024 *)