login
sigma(n) + n is a cube.
0

%I #10 Oct 22 2023 11:51:10

%S 13,76,280,4258,4719,4887,12207,13106,41823,42804,51671,54261,56283,

%T 65512,77671,95139,98219,135724,147440,149176,177911,220546,239599,

%U 279145,285347,285957,299432,308503,312137,335106,350739,525429,611123,634600,663377,700064

%N sigma(n) + n is a cube.

%e sigma(13) + 13 = 27 = 3^3.

%t Select[Range[701100],IntegerQ[Surd[DivisorSigma[1,#]+#,3]]&] (* _Harvey P. Dale_, Oct 22 2023 *)

%o (PARI) isok(n) = ispower(sigma(n) + n, 3); \\ _Michel Marcus_, Jan 22 2014

%Y Cf. A155085.

%K nonn

%O 1,1

%A _Giovanni Resta_, Feb 13 2006

%E More terms from _Michel Marcus_, Jan 22 2014