A036304 Composite numbers whose prime factors contain no digits other than 1 and 4.

121, 451, 1331, 1681, 4961, 14641, 18491, 45221, 48851, 54571, 68921, 125521, 158521, 161051, 168551, 182081, 203401, 452551, 455521, 467851, 485221, 497431, 537361, 590851, 600281, 758131, 1380731, 1686781, 1697851, 1743731, 1771561

Offset

1,1

Comments

All terms are a product of at least two terms of A020452. - 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 A020452} (p/(p - 1)) - Sum_{p in A020452} 1/p - 1 = 0.0122909749... . - Amiram Eldar, May 18 2022

Example

The composite 4961 = 11^2 * 41 is in the sequence as the digits of its prime factors are either 1 or 4. - David A. Corneth, Oct 17 2020

Crossrefs

Cf. A020452, A036302-A036325.

Sequence in context: A144719 A222551 A017282 * A052082 A062555 A017390

Adjacent sequences: A036301 A036302 A036303 * A036305 A036306 A036307

Keyword

nonn,easy,base

Author

Patrick De Geest, Dec 15 1998

Status

approved