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A036318 Composite numbers n such that digits of prime factors of n are either 4 or 7. 2
49, 329, 343, 2209, 2303, 2401, 15463, 16121, 16807, 31129, 52339, 103823, 108241, 112847, 117649, 209009, 217903, 313439, 334439, 351419, 366373, 523229, 542129, 542339, 544229, 726761, 757687, 789929, 823543, 1463063, 1525321, 2104519 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are a product of at least two terms of A020465. - David A. Corneth, Oct 09 2020

LINKS

David A. Corneth, Table of n, a(n) for n = 1..10000

Index entries sequences related to prime factors

MATHEMATICA

pf47Q[n_]:=Module[{u=Union[Flatten[IntegerDigits/@Transpose[ FactorInteger[ n]][[1]]]]}, !PrimeQ[n]&&(u=={4}||u=={7}||u=={4, 7})]; Select[ Range[ 2200000], pf47Q] (* Harvey P. Dale, Jun 05 2013 *)

CROSSREFS

Cf. A020465, A036302-A036325.

Sequence in context: A340124 A017474 A335389 * A020323 A036322 A036324

Adjacent sequences:  A036315 A036316 A036317 * A036319 A036320 A036321

KEYWORD

nonn,easy,base

AUTHOR

Patrick De Geest, Dec 15 1998

STATUS

approved

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Last modified March 7 14:00 EST 2021. Contains 341886 sequences. (Running on oeis4.)