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A088834 Numbers k such that sigma(k) == 6 (mod k). 7
1, 5, 6, 25, 180, 8925, 32445, 442365 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
For each integer j in A059609, 2^(j-1)*(2^j - 7) is in the sequence. E.g., for j = A059609(1) = 39 we get 151115727449904501489664. - M. F. Hasler and Farideh Firoozbakht, Dec 03 2013
No more terms to 10^10. - Charles R Greathouse IV, Dec 05 2013
a(9) > 10^13. - Giovanni Resta, Apr 02 2014
a(9) > 1.5*10^14. - Jud McCranie, Jun 02 2019
LINKS
Farideh Firoozbakht and M. F. Hasler, Variations on Euclid's formula for perfect numbers, Journal of Integer Sequences 13 (2010), 18 pp. Article ID 10.3.1.
EXAMPLE
Sigma(25) = 31 = 1*25 + 6, so 31 mod 25 = 6.
MATHEMATICA
Select[Range[1000000], Mod[DivisorSigma[1, #] - 6, #] == 0 &] (* T. D. Noe, Dec 03 2013 *)
PROG
(PARI) isok(n) = Mod(sigma(n), n) == 6; \\ Michel Marcus, Jan 03 2023
CROSSREFS
Cf. A087167 (a subsequence).
Cf. A059609.
Sequence in context: A038248 A046831 A003226 * A137081 A137079 A163658
KEYWORD
nonn,more
AUTHOR
Labos Elemer, Oct 29 2003
EXTENSIONS
Terms corrected by Charles R Greathouse IV and Farideh Firoozbakht, Dec 03 2013
STATUS
approved

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Last modified March 19 06:32 EDT 2024. Contains 370953 sequences. (Running on oeis4.)