A025624 Numbers of form 5^i*9^j, with i, j >= 0.

1, 5, 9, 25, 45, 81, 125, 225, 405, 625, 729, 1125, 2025, 3125, 3645, 5625, 6561, 10125, 15625, 18225, 28125, 32805, 50625, 59049, 78125, 91125, 140625, 164025, 253125, 295245, 390625, 455625, 531441, 703125, 820125, 1265625, 1476225, 1953125

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

Sum_{n>=1} 1/a(n) = (5*9)/((5-1)*(9-1)) = 45/32. - Amiram Eldar, Sep 24 2020

a(n) ~ exp(sqrt(2*log(5)*log(9)*n)) / sqrt(45). - Vaclav Kotesovec, Sep 24 2020

Mathematica

f[upto_]:=Module[{maxi=Ceiling[Log[5, upto]], maxj=Ceiling[Log[9, upto]], s}, s=Union[Flatten[Outer[Times, 5^Range[0, maxi], 9^Range[0, maxj]]]]; Select[s, #<=upto&]]; f[2000000] (* Harvey P. Dale, Mar 27 2011 *)

Crossrefs

Subsequence of A003593.

Sequence in context: A147192 A259665 A284285 * A147496 A147383 A276918

Adjacent sequences: A025621 A025622 A025623 * A025625 A025626 A025627

Keyword

easy,nonn

Author

David W. Wilson

Status

approved