A036322 Composite numbers whose prime factors contain no digits other than 6 and 7.

49, 343, 469, 2401, 3283, 4489, 4739, 16807, 22981, 31423, 33173, 45359, 117649, 160867, 219961, 232211, 300763, 317513, 458329, 474439, 536669, 537439, 823543, 1126069, 1539727, 1625477, 2105341, 2222591, 3039053, 3208303, 3321073

Offset

1,1

Comments

The multiplicative closure of A020469 consists of itself, 1, and this sequence. - Charles R Greathouse IV, Jun 25 2014

Links

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

Index entries for sequences related to prime factors.

Formula

Sum_{n>=1} 1/a(n) = Product_{p in A020469} (p/(p - 1)) - Sum_{p in A020469} 1/p - 1 = 0.0268448443... . - Amiram Eldar, May 22 2022

Crossrefs

Cf. A020469, A036302-A036325.

Sequence in context: A036318 A365206 A020323 * A036324 A211736 A211747

Adjacent sequences: A036319 A036320 A036321 * A036323 A036324 A036325

Keyword

nonn,easy,base

Author

Patrick De Geest, Dec 15 1998

Status

approved