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%I #9 Mar 28 2014 19:28:40
%S 4,6,25,18,51,91,32,125,161,209,221,75,215,287,407,527,551,98,175,335,
%T 671,767,1007,1247,1271,581,869,1241,1349,1541,1769,1829,1961,2021,
%U 545,749,1133,1313,1649,2573,2993,3053,3149,3233,243,791,1199,1391,1751,1919
%N Irregular triangle of numbers k that have A238895(n) as the sum of the proper divisors of each k.
%C It is interesting that these numbers have a very simple factorization. For example, the terms in row 6 factor as 3*5^2, 5*43, 7*41, 11*37, 17*31, and 19*29.
%H T. D. Noe, <a href="/A239625/b239625.txt">Rows n = 2..51 of irregular triangle, flattened</a>
%e The rows are
%e 1: {empty}
%e 2: 4,
%e 3: 6, 25,
%e 4: 18, 51, 91,
%e 5: 32, 125, 161, 209, 221,
%e 6: 75, 215, 287, 407, 527, 551,
%e 7: 98, 175, 335, 671, 767, 1007, 1247, 1271,
%e 8: 581, 869, 1241, 1349, 1541, 1769, 1829, 1961, 2021
%t nn = 200; s = Table[0, {nn}]; d = Table[DivisorSigma[1, n] - n, {n, (nn/2)^2}]; Do[If[0 < d[[n]] <= nn, s[[d[[n]]]]++], {n, (nn/2)^2}]; t = {}; mx = -1; Do[If[s[[n]] > mx, mx = s[[n]]; AppendTo[t, {n, mx}]], {n, 2, nn}]; t2 = Transpose[t][[1]]; Table[Flatten[Position[d, n]], {n, t2}]
%Y Cf. A238895.
%K nonn,tabf
%O 2,1
%A _T. D. Noe_, Mar 28 2014
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