A332838 Numbers k such that -tau(k)^2 == tau(k) mod k where tau = A000005.

1, 2, 3, 4, 10, 24, 156, 600

Offset

1,2

Links

Table of n, a(n) for n=1..8.

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: A132135 A131871 A132446 * A123700 A005433 A139009

Adjacent sequences: A332835 A332836 A332837 * A332839 A332840 A332841

Keyword

nonn,fini,full

Author

Juri-Stepan Gerasimov, Feb 26 2020

Status

approved