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

1,1

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]

Example

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

Mathematica

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

Prog

(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

Crossrefs

Cf. A195106, A111192; A143205 is a subsequence.

Sequence in context: A230125 A027865 A247681 * A143205 A111192 A063873

Adjacent sequences: A195115 A195116 A195117 * A195119 A195120 A195121

Keyword

nonn

Author

Reinhard Zumkeller, Sep 13 2011

Status

approved