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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

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

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Last modified August 17 23:13 EDT 2022. Contains 356204 sequences. (Running on oeis4.)