A025649 Exponent of 4 (value of i) in n-th number of form 4^i*10^j.

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

Offset

1,4

Links

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

Formula

a(n) = A235127(A025621(n)/10^A025686(n)). - Amiram Eldar, Nov 08 2025

Mathematica

seq[lim_] := SortBy[Flatten[Table[{i, j}, {i, 0, Log[4, lim]}, {j, 0, Log10[lim/4^i]}], 1], 4^#[[1]]*10^#[[2]] &][[;; , 1]]; seq[10^11] (* Amiram Eldar, Nov 08 2025 *)

Crossrefs

Cf. A025621, A235127.

A025686 is exponent of 10.

Differs from A025641 at a(114).

Sequence in context: A022328 A215344 A025641 * A025642 A384688 A025643

Adjacent sequences: A025646 A025647 A025648 * A025650 A025651 A025652

Keyword

nonn,easy

Author

David W. Wilson

Status

approved