A025648 Exponent of 4 (value of i) in n-th number of form 4^i*7^j.

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

Offset

1,4

Links

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

Formula

a(n) = A235127(A025619(n)). - Amiram Eldar, Nov 08 2025

Mathematica

seq[lim_] := IntegerExponent[Flatten[Table[4^i*7^j, {i, 0, Log[4, lim]}, {j, 0, Log[7, lim/4^i]}]] // Sort, 4]; seq[10^10] (* Amiram Eldar, Nov 08 2025 *)

Crossrefs

Cf. A025619, A025666, A235127.

Sequence in context: A255325 A391368 A025654 * A025655 A022336 A019586

Adjacent sequences: A025645 A025646 A025647 * A025649 A025650 A025651

Keyword

nonn,easy

Author

David W. Wilson

Status

approved