A036315 Composite numbers whose prime factors contain no digits other than 3 and 5.

9, 15, 25, 27, 45, 75, 81, 125, 135, 159, 225, 243, 265, 375, 405, 477, 625, 675, 729, 795, 1059, 1125, 1215, 1325, 1431, 1765, 1875, 2025, 2187, 2385, 2809, 3125, 3177, 3375, 3645, 3975, 4293, 5295, 5625, 6075, 6561, 6625, 7155, 8427, 8825, 9375, 9531

Offset

1,1

Comments

Products of at least two terms of A020462. - David A. Corneth, Oct 09 2020

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 A020462} (p/(p - 1)) - Sum_{p in A020462} 1/p - 1 = 0.3620363317... . - Amiram Eldar, May 22 2022

Mathematica

Select[Range[10000], SubsetQ[{3, 5}, Union[Flatten[IntegerDigits/@ FactorInteger[ #][[All, 1]]]]]&&CompositeQ[#]&] (* Harvey P. Dale, May 30 2021 *)

Crossrefs

Cf. A003593, A020462, A036302-A036325.

Sequence in context: A138193 A330947 A337237 * A340120 A020154 A079290

Adjacent sequences: A036312 A036313 A036314 * A036316 A036317 A036318

Keyword

nonn,easy,base

Author

Patrick De Geest, Dec 15 1998

Status

approved