A036310 Composite numbers whose prime factors contain no digits other than 2 and 3.

4, 6, 8, 9, 12, 16, 18, 24, 27, 32, 36, 46, 48, 54, 64, 69, 72, 81, 92, 96, 108, 128, 138, 144, 162, 184, 192, 207, 216, 243, 256, 276, 288, 324, 368, 384, 414, 432, 446, 466, 486, 512, 529, 552, 576, 621, 648, 669, 699, 729, 736, 768, 828, 864, 892, 932, 972

Offset

1,1

Comments

All terms are a product of at least two terms of A020458. - David A. Corneth, Oct 09 2020

Links

David A. Corneth, Table of n, a(n) for n = 1..10000 (first 1000 terms from Vincenzo Librandi)

Index entries for sequences related to prime factors.

Formula

Sum_{n>=1} 1/a(n) = Product_{p in A020458} (p/(p - 1)) - Sum_{p in A020458} 1/p - 1 = 1.2804224166... . - Amiram Eldar, May 18 2022

Mathematica

dpfQ[n_]:=Module[{d=Union[Flatten[IntegerDigits/@Transpose[ FactorInteger[ n]][[1]]]]}, !PrimeQ[n] && (d=={2}||d=={3}||d=={2, 3})]; Select[Range[ 1000], dpfQ] (* Harvey P. Dale, Aug 24 2013 *)

Crossrefs

Cf. A003586, A020458, A036302-A036325.

Sequence in context: A200878 A344030 A350706 * A046760 A115684 A020201

Adjacent sequences: A036307 A036308 A036309 * A036311 A036312 A036313

Keyword

nonn,easy,base

Author

Patrick De Geest, Dec 15 1998

Status

approved