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A224488 Numbers m such that k*m = Sum_{j|m, j < m} 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
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 &]
PROG
(PARI) isok(m) = sumdiv(m, d, if (d!=m, sigma(d))) % m == 0; \\ Michel Marcus, Jul 13 2021
CROSSREFS
Sequence in context: A220817 A346889 A114918 * A149213 A149214 A149215
KEYWORD
nonn,more
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 March 29 02:16 EDT 2024. Contains 371264 sequences. (Running on oeis4.)