A025644 Exponent of 3 (value of i) in n-th number of form 3^i*10^j.

0, 1, 2, 0, 3, 1, 4, 2, 0, 5, 3, 1, 6, 4, 2, 0, 7, 5, 3, 1, 8, 6, 4, 2, 0, 9, 7, 5, 3, 1, 10, 8, 6, 4, 2, 0, 11, 9, 7, 5, 3, 1, 12, 10, 8, 6, 4, 2, 0, 13, 11, 9, 7, 5, 3, 1, 14, 12, 10, 8, 6, 4, 2, 0, 15, 13, 11, 9, 7, 5, 3, 1, 16, 14, 12, 10, 8, 6, 4, 2, 0, 17, 15, 13, 11, 9, 7, 5, 3, 1, 18, 16, 14, 12, 10

Offset

1,3

Comments

Starts like A082375 but the pattern then becomes more irregular ..., 5, 3, 1, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 23, 0, 21, 19, 17, 15, 13, 11, 9, 7, 5, 3, 24, 1, 22, 20, ... - R. J. Mathar, Aug 27 2025

Links

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

Formula

a(n) = A007949(A025616(n)). - Amiram Eldar, Nov 08 2025

Mathematica

seq[lim_] := IntegerExponent[Flatten[Table[3^i*10^j, {i, 0, Log[3, lim]}, {j, 0, Log10[lim/3^i]}]] // Sort, 3]; seq[10^9] (* Amiram Eldar, Nov 08 2025 *)

Crossrefs

Cf. A007949, A025616, A025685, A082375.

Sequence in context: A063277 A029178 A082375 * A022332 A215589 A274185

Adjacent sequences: A025641 A025642 A025643 * A025645 A025646 A025647

Keyword

nonn,easy

Author

David W. Wilson

Status

approved