A209237 Number of practical numbers not exceeding 2^n.

1, 2, 3, 5, 7, 13, 21, 36, 61, 113, 202, 368, 667, 1218, 2268, 4222, 7959, 15057, 28480, 53742, 101770, 193406, 368610, 703596, 1347122, 2587174, 4981200, 9602184, 18548787, 35847883, 69321177

Offset

0,2

Comments

Motivated by Sun's conjecture concerning the asymptotics of A005153.

Up to 10^6, there are 97385 (9.7%), up to 10^7 there are 829157 (8.3%) practical numbers.

Links

Table of n, a(n) for n=0..30.

Prog

(PARI) a(n)=sum(k=1, 2^(n-1), is_A005153(2*k), 1)

Crossrefs

Cf. A005153.

Sequence in context: A119717 A000627 A337270 * A322475 A181526 A163487

Adjacent sequences: A209234 A209235 A209236 * A209238 A209239 A209240

Keyword

nonn,more

Author

M. F. Hasler, Jan 13 2013

Extensions

a(26)-a(30) from Jinyuan Wang, Mar 02 2020

Status

approved