A025646 Exponent of 4 (value of i) in n-th number of form 4^i*5^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, 8, 0, 7, 6, 5, 4, 3, 2, 9, 1, 8, 0, 7, 6, 5, 4, 3, 10, 2, 9, 1, 8, 0, 7, 6, 5, 4, 11, 3, 10, 2, 9, 1, 8, 0, 7, 6, 5, 12, 4, 11, 3, 10, 2, 9, 1, 8, 0, 7, 6, 13, 5, 12, 4, 11, 3, 10, 2, 9, 1, 8, 0, 7, 14, 6, 13

Offset

1,4

Links

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

Index entries for sequences which agree for a long time but are different.

Formula

a(n) = A235127(A025617(n)). - Amiram Eldar, Jul 09 2025

Mathematica

With[{nn=15}, IntegerExponent[#, 4]&/@Union[Flatten[Table[4^x 5^y, {x, 0, nn}, {y, 0, nn}]]]] (* Harvey P. Dale, May 10 2019 *)
With[{max = 10^10}, IntegerExponent[Sort[Flatten[Table[4^i*5^j, {i, 0, Log[4, max]}, {j, 0, Log[5, max/4^i]}]]], 4]] (* Amiram Eldar, Jul 09 2025 *)

Crossrefs

Cf. A025617, A025650, A235127.

Differs from A025661 at a(1881).

Sequence in context: A330238 A025670 A122200 * A025661 A025671 A025652

Adjacent sequences: A025643 A025644 A025645 * A025647 A025648 A025649

Keyword

nonn

Author

David W. Wilson

Status

approved