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A224488 Numbers n such that k*n = sum_{j divides n, j < n} sigma(j), where k>=1 is an integer. 2
4, 10, 42, 90, 2448, 4680, 27144, 117000, 154498509, 222970077, 11049088050, 63554826816 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(13) > 10^11.

LINKS

Table of n, a(n) for n=1..12.

EXAMPLE

The divisors of 10 smaller than 10 are 1, 2 and 5. Since sigma(1) + sigma(2) + sigma(5) = 10, 10 is in the sequence.

MATHEMATICA

Select[Range[2, 120000], Mod[Total@DivisorSigma[1, Most@Divisors@#], #] == 0 &]

CROSSREFS

Cf. A221219.

Sequence in context: A222367 A220817 A114918 * A149213 A149214 A149215

Adjacent sequences:  A224485 A224486 A224487 * A224489 A224490 A224491

KEYWORD

nonn

AUTHOR

Giovanni Resta, Apr 08 2013

EXTENSIONS

a(9)-a(12) and bound on a(13) from Donovan Johnson.

STATUS

approved

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Last modified December 5 15:11 EST 2019. Contains 329753 sequences. (Running on oeis4.)