A002270 Composite numbers k such that k*sigma(k) == 2 (mod phi(k)).

4, 6, 22

Offset

1,1

Comments

Composite terms of A051948.

References

J. Roberts, Lure of the Integers, Math. Assoc. America, 1992, p. 147.

M. V. Subbarao, On two congruences for primality. Pacific J. Math. 52 (1974), 261-268.

Links

Table of n, a(n) for n=1..3.

Mathematica

Select[Range[4, 100], ! PrimeQ[#] && Mod[#*DivisorSigma[1, # ] - 2 , EulerPhi[#]] == 0 &] (* Jean-François Alcover, Sep 16 2013 *)

Crossrefs

Cf. A051948.

Sequence in context: A151520 A282517 A227249 * A286358 A088228 A272309

Adjacent sequences: A002267 A002268 A002269 * A002271 A002272 A002273

Keyword

nonn,fini,full,bref

Author

N. J. A. Sloane

Extensions

Definition corrected by Tanya Khovanova, Nov 05 2007

Status

approved