A025686 - OEIS

A025686

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

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

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OFFSET

1,7

LINKS

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

FORMULA

a(n) = A122840(A025621(n)). - Amiram Eldar, Nov 09 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]] &][[;; , 2]]; seq[10^11] (* Amiram Eldar, Nov 09 2025 *)

CROSSREFS

Cf. A025621, A122840.

A025649 is the exponent of 4.

Differs from A025657 at a(114).

Sequence in context: A091917 A391262 A025657 * A215345 A022329 A087466

Adjacent sequences: A025683 A025684 A025685 * A025687 A025688 A025689

KEYWORD

nonn,easy

AUTHOR

David W. Wilson

STATUS

approved