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Search: id:A072108
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| A072108 |
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Least k such that sum(i=1,k,gcd(k,i)) = n * sigma(k). |
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+0
1
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| 1, 40, 220, 980, 2940, 11016, 10080, 44064, 55080, 112000
(list; graph; listen)
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OFFSET
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1,2
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MATHEMATICA
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f[n_] := Block[{k = 1}, While[ Sum[ GCD[k, i], {i, 1, k}] != n*DivisorSigma[1, k], k++ ]; k]
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PROGRAM
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(PARI) for(n=1, 5, k=1; while(abs(sum(i=1, k, gcd(k, i))-sigma(k)*n)>0, k++); print1(k, ", "))
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CROSSREFS
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Sequence in context: A117216 A077818 A111176 this_sequence A074360 A068790 A073962
Adjacent sequences: A072105 A072106 A072107 this_sequence A072109 A072110 A072111
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KEYWORD
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more,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Jun 19 2002
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 28 2002 and Jul 09 2002
Corrected and extended by Rick L. Shepherd (rshepherd2(AT)hotmail.com), Jun 30 2002
a(10) from Robert G. Wilson v (rgwv(AT)rgwv.com), Jul 09 2002
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