A025683 Exponent of 9 (value of i) in n-th number of form 9^i*10^j.

0, 1, 0, 2, 1, 0, 3, 2, 1, 0, 4, 3, 2, 1, 0, 5, 4, 3, 2, 1, 0, 6, 5, 4, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 8, 7, 6, 5, 4, 3, 2, 1, 0, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3

Offset

1,4

Links

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

Formula

a(n) = A007949(A025635(n))/2. - Amiram Eldar, Nov 09 2025

Mathematica

seq[lim_] := IntegerExponent[Flatten[Table[9^i*10^j, {i, 0, Log[9, lim]}, {j, 0, Log10[lim/9^i]}]] // Sort, 9]; seq[10^13] (* Amiram Eldar, Nov 09 2025 *)

Crossrefs

Cf. A007949, A025635, A025691.

Differs from A025581 at a(253).

Sequence in context: A025581 A025669 A025676 * A025660 A025677 A025651

Adjacent sequences: A025680 A025681 A025682 * A025684 A025685 A025686

Keyword

nonn,easy

Author

David W. Wilson

Extensions

Incorrect Mathematica program removed by Amiram Eldar, Nov 09 2025

Status

approved