A072108 Least k such that Sum_{i=1..k} gcd(k,i) = n * sigma(k).

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

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