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A195118
Numbers with largest and smallest prime factors differing by 6.
4
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
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
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Sep 13 2011
STATUS
approved