A073495 Numbers having exactly three prime gaps in their factorization.

1870, 2090, 2470, 2530, 2990, 3190, 3410, 3458, 3740, 3770, 3910, 4030, 4070, 4180, 4186, 4510, 4730, 4810, 4930, 4940, 5060, 5170, 5187, 5270, 5278, 5330, 5474, 5510, 5590, 5642, 5830, 5890, 5980, 6110, 6279, 6290, 6380, 6490, 6710, 6734, 6820, 6890

Offset

1,1

Links

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

Formula

A073490(a(n)) = 3.

Example

1870 is a term, as 1870 = 2*5*11*17 with three gaps: between 2 and 5, between 5 and 11 and between 11 and 17.

Mathematica

q[n_] := SequenceCount[FactorInteger[n][[;; , 1]], {p1_, p2_} /; p2 != NextPrime[p1], Overlaps -> True] == 3; Select[Range[7000], q] (* Amiram Eldar, Apr 10 2021*)

Prog

(Haskell)
a073495 n = a073495_list !! (n-1)
a073495_list = filter ((== 3) . a073490) [1..]
-- Reinhard Zumkeller, Dec 20 2013

Crossrefs

Cf. A005117, A073490, A073492, A073493, A073494, A073489.

Sequence in context: A237152 A306864 A306877 * A073489 A353552 A232040

Adjacent sequences: A073492 A073493 A073494 * A073496 A073497 A073498

Keyword

nonn

Author

Reinhard Zumkeller, Aug 03 2002

Status

approved