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URL: https://oeis.org/A332838

⇱ A332838 - OEIS

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A332838
Numbers k such that -tau(k)^2 == tau(k) mod k where tau = A000005.
0
1, 2, 3, 4, 10, 24, 156, 600
OFFSET
1,2
EXAMPLE
24 is in this sequence because tau(24) = 8 and -8^2 mod 24 = 8.
MAPLE
q:= n-> (t-> irem(t^2+t, n)=0)(numtheory[tau](n)):
select(q, [$1..1000])[]; # Alois P. Heinz, Feb 26 2020
MATHEMATICA
Select[Range[1000], Divisible[(d = DivisorSigma[0, #]) + d^2, #] &] (* Amiram Eldar, Feb 26 2020 *)
PROG
(PARI) isok(m) = my(nd=numdiv(m)); Mod(-nd^2, m) == nd; \\ Michel Marcus, Feb 26 2020
CROSSREFS
Cf. A000005.
Sequence in context: A372933 A131871 A132446 * A123700 A005433 A139009
KEYWORD
nonn,fini,full
AUTHOR
STATUS
approved