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Search: id:A113654
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| A113654 |
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Numbers n such that the square of n contains sigma(n) as a substring, in base 10. |
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+0
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| 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
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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If p=180...01 is prime, then n=2*5*p=180...010, n^2=3240...0360...0100 and sigma(n)=3240...036, thus n belongs to the sequence.
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EXAMPLE
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153^2=23409 and sigma(153)=234.
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MATHEMATICA
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lst = {}; Do[If[{}!= StringPosition[ToString[n^2], ToString@DivisorSigma[1, n]], AppendTo[lst, n]], {n, 10^6}]; lst
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CROSSREFS
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Sequence in context: A155075 A062697 A062696 this_sequence A066592 A159613 A062332
Adjacent sequences: A113651 A113652 A113653 this_sequence A113655 A113656 A113657
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KEYWORD
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base,nonn
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AUTHOR
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Giovanni Resta (g.resta(AT)iit.cnr.it), Jan 26 2006
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