A088830 - OEIS

%I #29 Oct 02 2024 12:17:33

%S 1,35,15,14,56,6,12,42,30,168,2580,210,630,420,840,20790,416640,9240,

%T 291060,83160,120120,5165160,1719277560,43825320,26860680,277560360,

%U 1304863560,569729160,587133466920,16522145640,33044291280,563462139240,1140028049160

%N a(n) = Min{x : sigma(x) = n*phi(x), x is not a prime}, the least nonprime solutions to sigma(x) = n*phi(x); special balanced numbers.

%C a(33) > 10^12. - _Donovan Johnson_, Sep 03 2013

%C a(34) <= 9015394227840, a(35) <= 1255683068640. - _Giovanni Resta_, May 08 2017

%H Amiram Eldar, <a href="/A088830/b088830.txt">Table of n, a(n) for n = 1..36</a> (calculated using data from Jud McCranie)

%F For n > 3, a(n) = A055234(n). - _David Wasserman_, Aug 18 2005

%t ds[x_, de_] := DivisorSigma[1, x]-de*EulerPhi[x] a[n_] := Block[{m=1, s=ds[m, n]}, While[(s !=0||PrimeQ[m])&&!Greater[m, 100000], m++ ]; m]; Table[a[n], {n, 22}]

%Y Compare A087979, which has a slightly different definition.

%Y Cf. A074891, A000203, A000010, A087979, A020492.

%Y Cf. A055234.

%K nonn

%O 1,2

%A _Labos Elemer_, Nov 03 2003

%E More terms from _David Wasserman_, Aug 18 2005

%E a(32) from _Donovan Johnson_, Sep 03 2013

%E a(33) from _Giovanni Resta_, May 08 2017