A073494 Numbers having exactly two prime gaps in their factorization.

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

Offset

1,1

Comments

A073490(a(n)) = 2.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

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..]
-- Reinhard Zumkeller, Dec 20 2013

Crossrefs

Cf. A005117, A073492, A073493, A073495, A073488.

Sequence in context: A275343 A059469 A114068 * A073488 A244389 A176879

Adjacent sequences: A073491 A073492 A073493 * A073495 A073496 A073497

Keyword

nonn

Author

Reinhard Zumkeller, Aug 03 2002

Status

approved