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A036322 Composite numbers whose prime factors contain no digits other than 6 and 7. 2
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 (list; graph; refs; listen; history; text; internal format)
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: A335389 A036318 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

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Last modified August 12 04:52 EDT 2022. Contains 356067 sequences. (Running on oeis4.)