Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #9 Nov 27 2014 04:07:54
%S 12,24,78,66,54,42,30,120,540,390,264,282,366,180,546,510,330,318,990,
%T 936,702,780,564,1290,870,528,312,168,222,150,138,5778,6174,3432,3150,
%U 2850,2190,8432,4464,3472,2480,1488,5430,6750,4452,4396,4650,3270,2712
%N a(n) is the smallest number that is precisely n-tuply abundant.
%C See A081705 for the definition of n-tuply abundant. - _David Wasserman_, Jun 24 2004
%e a(3)=78 because 78 is the smallest number that is exactly triply abundant, with this aliquot chain: 78->90->144->259->45.
%o (PARI) LIMIT = 50; A = vector(LIMIT); count = 0; i = 1; while (count < LIMIT, i = i + 1; ab = 0; lastn = i; n = sigma(i) - i; while(ab <= LIMIT && n > lastn, ab = ab + 1; lastn = n; n = sigma(lastn) - n); if(ab <= LIMIT && ab > 0 && A[ab] == 0, A[ab] = i; count = count + 1)); A \\ _David Wasserman_, Jun 24 2004
%Y Cf. A081705, A081699.
%K nonn
%O 1,1
%A Gabriel Cunningham (gcasey(AT)mit.edu), Apr 08 2003
%E More terms from _David Wasserman_, Jun 24 2004