A078662 Number of balanced numbers <= 2^n.

1, 2, 3, 4, 7, 8, 11, 14, 19, 24, 33, 39, 54, 69, 91, 122, 160, 206, 270, 346, 451, 575, 737, 962, 1260, 1635, 2110, 2712, 3491, 4564, 5942, 7773, 10195, 13357, 17441, 22920, 30093, 39658, 52199, 68635, 90390, 118897, 156393, 206293, 272105, 359270, 473917, 626919, 830490, 1099174

Offset

0,2

Links

Table of n, a(n) for n=0..49.

Example

There are nine balanced numbers between 512 and 1024: {570, 594, 616, 630, 714, 744, 812, 840, 910}, so a(10) = 9 + a(9) = 33.

Mathematica

k = 1; c = 0; Do[ While[k <= 2^n, If[ IntegerQ[ DivisorSigma[1, k]/EulerPhi[k]], c++ ]; k++ ]; Print[c], {n, 0, 24}]

Crossrefs

Cf. A020492.

Partial sums of A078555.

Sequence in context: A225229 A239389 A256219 * A050048 A122456 A186243

Adjacent sequences: A078659 A078660 A078661 * A078663 A078664 A078665

Keyword

nonn

Author

Labos Elemer, Dec 06 2002

Extensions

More terms from Robert G. Wilson v, Dec 14 2002

a(25)-a(37) from Donovan Johnson, Mar 03 2013

a(38)-a(49) from Amiram Eldar, Jun 04 2024

Status

approved