A036306 Composite numbers whose prime factors contain no digits other than 1 and 6.

121, 671, 1331, 3721, 7271, 7381, 14641, 40321, 40931, 73271, 79981, 81191, 122771, 161051, 177221, 183271, 226981, 406321, 436921, 443531, 450241, 680821, 727771, 805981, 879791, 893101, 982771, 1016321, 1227721, 1350481, 1771561

Offset

1,1

Comments

All terms are a product of at least two terms of A020454. - David A. Corneth, Oct 09 2020

Links

David A. Corneth, Table of n, a(n) for n = 1..10000 (first 1000 terms from Alois P. Heinz)

Index entries for sequences related to prime factors.

Formula

Sum_{n>=1} 1/a(n) = Product_{p in A020454} (p/(p - 1)) - Sum_{p in A020454} 1/p - 1 = 0.0112607346... . - Amiram Eldar, May 18 2022

Mathematica

pf16Q[n_]:=Module[{pfs=Union[Flatten[IntegerDigits/@Transpose[ FactorInteger[ n]][[1]]]]}, pfs=={1}||pfs=={1, 6}]; Select[Range[ 2*10^6], CompositeQ[#]&&pf16Q[#]&] (* Harvey P. Dale, Jul 12 2014 *)

Crossrefs

Cf. A020454, A036302-A036325.

Sequence in context: A307798 A204034 A183885 * A014749 A262051 A048950

Adjacent sequences: A036303 A036304 A036305 * A036307 A036308 A036309

Keyword

nonn,easy,base

Author

Patrick De Geest, Dec 15 1998

Status

approved