A072108 - OEIS

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

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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