A025679 - OEIS

A025679

Exponent of 9 (value of j) in n-th number of form 5^i*9^j.

0, 0, 1, 0, 1, 2, 0, 1, 2, 0, 3, 1, 2, 0, 3, 1, 4, 2, 0, 3, 1, 4, 2, 5, 0, 3, 1, 4, 2, 5, 0, 3, 6, 1, 4, 2, 5, 0, 3, 6, 1, 4, 7, 2, 5, 0, 3, 6, 1, 4, 7, 2, 5, 8, 0, 3, 6, 1, 4, 7, 2, 5, 8, 0, 3, 6, 9, 1, 4, 7, 2, 5, 8, 0, 3, 6, 9, 1, 4, 7, 10, 2, 5, 8, 0, 3, 6, 9, 1, 4, 7, 10, 2, 5, 8, 0, 11, 3, 6, 9, 1, 4, 7, 10, 2, 5

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OFFSET

1,6

LINKS

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

FORMULA

a(n) = A007949(A025624(n))/2. - Amiram Eldar, Nov 09 2025

MATHEMATICA

seq[lim_] := IntegerExponent[Flatten[Table[5^i*9^j, {i, 0, Log[5, lim]}, {j, 0, Log[9, lim/5^i]}]] // Sort, 9]; seq[10^12] (* Amiram Eldar, Nov 09 2025 *)

CROSSREFS

Cf. A007949, A025624, A025654.

Sequence in context: A022337 A025687 A025666 * A071491 A156537 A239501

Adjacent sequences: A025676 A025677 A025678 * A025680 A025681 A025682

KEYWORD

nonn,easy

AUTHOR

David W. Wilson

STATUS

approved