OFFSET
1,9
COMMENTS
Terms 0 .. k occur for the first time at n = 1, 2, 9, 25, 133, 253, 559, 2159, 2489, 3151, 5597, 7967, ..., which after 2 seem all to be semiprimes, that is, A156552(n) has binary weight 2.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000 (based on Hans Havermann's factorization of A156552)
FORMULA
PROG
(PARI)
A156552(n) = {my(f = factor(n), p2 = 1, res = 0); for(i = 1, #f~, p = 1 << (primepi(f[i, 1]) - 1); res += (p * p2 * (2^(f[i, 2]) - 1)); p2 <<= f[i, 2]); res}; \\ From A156552
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Mar 28 2019
STATUS
approved