OFFSET
1,2
COMMENTS
If p = 180...01 is prime, then k = 2*5*p = 180...010, k^2 = 3240...0360...0100 and sigma(k) = 3240...036, thus k belongs to the sequence.
EXAMPLE
153^2 = 23409 and sigma(153) = 234.
MATHEMATICA
lst = {}; Do[If[{}!= StringPosition[ToString[n^2], ToString@DivisorSigma[1, n]], AppendTo[lst, n]], {n, 10^6}]; lst
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Giovanni Resta, Jan 26 2006
STATUS
approved