|
|
A073494
|
|
Numbers having exactly two prime gaps in their factorization.
|
|
6
|
|
|
110, 130, 170, 182, 190, 220, 230, 238, 260, 266, 273, 290, 310, 322, 340, 357, 364, 370, 374, 380, 399, 406, 410, 418, 430, 434, 440, 460, 470, 476, 483, 494, 506, 518, 520, 530, 532, 546, 550, 561, 574, 580, 590, 598, 602, 609, 610, 620, 627, 638, 644
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
|
|
LINKS
|
|
|
EXAMPLE
|
220 is a term, as 220 = 2*2*5*11 with two gaps: between 2 and 5 and between 5 and 11.
|
|
MATHEMATICA
|
pa[n_, k_] := If[k == NextPrime[n], 0, 1]; Select[Range[645], Total[pa @@@ Partition[First /@ FactorInteger[#], 2, 1]] == 2 &] (* Jayanta Basu, Jul 01 2013 *)
|
|
PROG
|
(Haskell)
a073494 n = a073494_list !! (n-1)
a073494_list = filter ((== 2) . a073490) [1..]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|