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

Author

Reinhard Zumkeller, Aug 03 2002

Keywords

• nonn

Comments

A073490(a(n)) = 2.

Examples

			220 is a term, as 220 = 2*2*5*11 with two gaps: between 2 and 5 and between 5 and 11.
		

Links

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

Crossrefs

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

Programs

Haskell

a073494 n = a073494_list !! (n-1)
a073494_list = filter ((== 2) . a073490) [1..]
-- Reinhard Zumkeller, Dec 20 2013

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 *)