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A248150 Numbers whose sum of divisors (A000203) is divisible by 4. 6
3, 6, 7, 11, 12, 14, 15, 19, 21, 22, 23, 24, 27, 28, 30, 31, 33, 35, 38, 39, 42, 43, 44, 46, 47, 48, 51, 54, 55, 56, 57, 59, 60, 62, 63, 65, 66, 67, 69, 70, 71, 75, 76, 77, 78, 79, 83, 84, 85, 86, 87, 88, 91, 92, 93, 94, 95, 96, 99, 102, 103, 105, 107, 108, 110, 111, 112, 114, 115, 118 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A subsequence of A028983 (even sum of divisors) which contains all numbers but the squares and twice the squares, so no term of this sequence is of that form, either.

Any number having at least two odd prime factors to an odd power is in this sequence, therefore it has asymptotic density 1. - M. F. Hasler, Apr 26 2017

LINKS

Table of n, a(n) for n=1..70.

FORMULA

a(n) ~ n. - Charles R Greathouse IV, Sep 01 2015

MATHEMATICA

Select[Range[200], Divisible[DivisorSigma[1, #], 4]&] (* Harvey P. Dale, Feb 20 2015 *)

PROG

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

CROSSREFS

Cf. A000203, A028982, A028983, A248151.

Sequence in context: A136272 A101184 A087643 * A022544 A194366 A091067

Adjacent sequences:  A248147 A248148 A248149 * A248151 A248152 A248153

KEYWORD

nonn

AUTHOR

M. F. Hasler, Oct 02 2014

STATUS

approved

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Last modified May 19 10:36 EDT 2019. Contains 323390 sequences. (Running on oeis4.)