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 A072108 Least k such that sum(i=1,k,gcd(k,i)) = n * sigma(k). 1
 1, 40, 220, 980, 2940, 11016, 10080, 44064, 55080, 112000, 245344, 220320, 308448, 484704, 550368, 2590720, 38509344, 1349460, 3248000, 7772160, 2423520, 5464480, 51482340, 14837760, 6301152, 18135040, 19872864, 10795680, 61116768, 45323520, 120513096, 67298560, 32387040, 118295408, 49660128, 86526720, 147671040, 225392640, 105754880, 92252160, 939050112, 163215360 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(97) <= 823547648000. - Hiroaki Yamanouchi, Jul 08 2014 LINKS Hiroaki Yamanouchi, Table of n, a(n) for n = 1..96 MATHEMATICA f[n_] := Block[{k = 1}, While[ Sum[ GCD[k, i], {i, 1, k}] != n*DivisorSigma[1, k], k++ ]; k] PROG (PARI) for(n=1, 5, k=1; while(abs(sum(i=1, k, gcd(k, i))-sigma(k)*n)>0, k++); print1(k, ", ")) CROSSREFS Sequence in context: A235270 A181637 A111176 * A218404 A235010 A235290 Adjacent sequences: A072105 A072106 A072107 * A072109 A072110 A072111 KEYWORD nonn AUTHOR Benoit Cloitre, Jun 19 2002 EXTENSIONS More terms from Robert G. Wilson v, Jun 28 2002 and Jul 09 2002 Corrected and extended by Rick L. Shepherd, Jun 30 2002 a(10) from Robert G. Wilson v, Jul 09 2002 a(11)-a(42) from Robert Gerbicz, Nov 24 2010 STATUS approved

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Last modified January 28 07:59 EST 2023. Contains 359850 sequences. (Running on oeis4.)