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.
FORMULA
a(n) = 1 + Sum_{k=0..n-1} A214932(k). - Amiram Eldar, May 05 2024
a(n) = A225559(2^n). - David A. Corneth, May 05 2024
PROG
(PARI) a(n)=sum(k=1, 2^(n-1), is_A005153(2*k), 1)
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, Jan 13 2013
EXTENSIONS
a(26)-a(30) from Jinyuan Wang, Mar 02 2020
a(31)-a(37) from Amiram Eldar, May 05 2024
STATUS
approved