

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
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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

M. F. Hasler, Table of n, a(n) for n = 1..1000


PROG

(PARI) for(n=1, 999, sigma(n)%4&&print1(n", "))


CROSSREFS

Cf. A000203 (sum of divisors), A028982, A028983, A248150.
Sequence in context: A269176 A091072 A001481 * A245226 A034026 A125022
Adjacent sequences: A248148 A248149 A248150 * A248152 A248153 A248154


KEYWORD

nonn


AUTHOR

M. F. Hasler, Oct 02 2014


STATUS

approved



