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A113654
Numbers k such that the square of k contains sigma(k) as a substring, in base 10.
0
1, 11, 101, 125, 153, 1205, 1502, 1810, 3080, 7631, 18010, 18650, 21020, 36559, 36911, 44805, 53999, 60541, 68443, 120005, 189585, 210020, 487195, 1059449, 1750004, 1800010, 1860050, 1872250, 2072139, 2170100, 2268661, 2496750
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
Sequence in context: A303570 A208262 A062696 * A066592 A316604 A208362
KEYWORD
base,nonn
AUTHOR
Giovanni Resta, Jan 26 2006
STATUS
approved