|
|
A248151
|
|
Numbers n such that the sum of the divisors of n is not divisible by 4.
|
|
5
|
|
|
1, 2, 4, 5, 8, 9, 10, 13, 16, 17, 18, 20, 25, 26, 29, 32, 34, 36, 37, 40, 41, 45, 49, 50, 52, 53, 58, 61, 64, 68, 72, 73, 74, 80, 81, 82, 89, 90, 97, 98, 100, 101, 104, 106, 109, 113, 116, 117, 121, 122, 128, 136, 137, 144, 146, 148, 149, 153, 157, 160, 162, 164, 169, 173, 178, 180
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
The complement of A248150; contains in particular A028982, the squares and twice the squares, for which sigma is odd.
The terms cannot have more than one odd prime factor to an odd power. Therefore this set has asymptotic density zero. The sequence grows faster than .75 n log(n). In particular: a(10) = 17, a(100) = 298, a(10^3) = 4724, a(10^4) = 66533, a(10^5) = 872434, a(10^6) = 10819205. - M. F. Hasler, Apr 26 2017
|
|
LINKS
|
|
|
PROG
|
(PARI) for(n=1, 999, sigma(n)%4&&print1(n", "))
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|