A025619 Numbers of form 4^i*7^j, with i, j >= 0.

1, 4, 7, 16, 28, 49, 64, 112, 196, 256, 343, 448, 784, 1024, 1372, 1792, 2401, 3136, 4096, 5488, 7168, 9604, 12544, 16384, 16807, 21952, 28672, 38416, 50176, 65536, 67228, 87808, 114688, 117649, 153664, 200704, 262144, 268912, 351232, 458752, 470596

Offset: 1

Author

David W. Wilson

Keywords

• easy
• nonn

Links

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

Crossrefs

Subsequence of A003591.

Programs

Mathematica

n=10^6; Flatten[Table[4^i*7^j, {i, 0, Log[4, n]}, {j, 0, Log[7, n/4^i]}]]//Sort (* Amiram Eldar, Sep 24 2020 *)

Formula

Sum_{n>=1} 1/a(n) = (4*7)/((4-1)*(7-1)) = 14/9. - Amiram Eldar, Sep 24 2020

a(n) ~ exp(sqrt(2*log(4)*log(7)*n)) / sqrt(28). - Vaclav Kotesovec, Sep 24 2020

a(n) = 4^A025648(n) * 7^A025666(n). - R. J. Mathar, Jul 06 2025