A025666 Exponent of 7 (value of j) in n-th number of form 4^i*7^j.

0, 0, 1, 0, 1, 2, 0, 1, 2, 0, 3, 1, 2, 0, 3, 1, 4, 2, 0, 3, 1, 4, 2, 0, 5, 3, 1, 4, 2, 0, 5, 3, 1, 6, 4, 2, 0, 5, 3, 1, 6, 4, 2, 7, 0, 5, 3, 1, 6, 4, 2, 7, 0, 5, 3, 8, 1, 6, 4, 2, 7, 0, 5, 3, 8, 1, 6, 4, 9, 2, 7, 0, 5, 3, 8, 1, 6, 4, 9, 2, 7, 0, 5, 10, 3, 8, 1, 6, 4, 9, 2, 7, 0, 5, 10, 3, 8, 1, 6, 11, 4, 9, 2, 7, 0, 5

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A025619, A025648.

Programs

Maple

N:= 10^10: # to consider all terms with 4^i*7^j<=N
S:= {seq(seq(4^i*7^j, j=0..floor(log[7](N/4^i))),i=0..floor(log[4](N)))}:
map(padic:-ordp, sort(convert(S,list)),7); # Robert Israel, Aug 11 2019

Formula

4^A025648(n)*7^a(n) = A025619(n). - Robert Israel, Aug 11 2019