A072108 - OEIS

%I #30 Sep 02 2024 17:13:14

%S 1,40,220,980,2940,11016,10080,44064,55080,112000,245344,220320,

%T 308448,484704,550368,2590720,38509344,1349460,3248000,7772160,

%U 2423520,5464480,51482340,14837760,6301152,18135040,19872864,10795680,61116768,45323520,120513096,67298560,32387040,118295408,49660128,86526720,147671040,225392640,105754880,92252160,939050112,163215360

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

%C a(97) <= 823547648000. - _Hiroaki Yamanouchi_, Jul 08 2014

%H Hiroaki Yamanouchi, <a href="/A072108/b072108.txt">Table of n, a(n) for n = 1..96</a>

%t f[n_] := Block[{k = 1}, While[ Sum[ GCD[k, i], {i, 1, k}] != n*DivisorSigma[1, k], k++ ]; k]

%o (PARI) for(n=1,5,k=1; while(abs(sum(i=1,k,gcd(k,i))-sigma(k)*n)>0,k++); print1(k,","))

%K nonn

%O 1,2

%A _Benoit Cloitre_, Jun 19 2002

%E More terms from _Robert G. Wilson v_, Jun 28 2002 and Jul 09 2002

%E Corrected and extended by _Rick L. Shepherd_, Jun 30 2002

%E a(10) from _Robert G. Wilson v_, Jul 09 2002

%E a(11)-a(42) from _Robert Gerbicz_, Nov 24 2010