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A239625
Irregular triangle of numbers k that have A238895(n) as the sum of the proper divisors of each k.
2
4, 6, 25, 18, 51, 91, 32, 125, 161, 209, 221, 75, 215, 287, 407, 527, 551, 98, 175, 335, 671, 767, 1007, 1247, 1271, 581, 869, 1241, 1349, 1541, 1769, 1829, 1961, 2021, 545, 749, 1133, 1313, 1649, 2573, 2993, 3053, 3149, 3233, 243, 791, 1199, 1391, 1751, 1919
OFFSET
2,1
COMMENTS
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.
EXAMPLE
The rows are
1: {empty}
2: 4,
3: 6, 25,
4: 18, 51, 91,
5: 32, 125, 161, 209, 221,
6: 75, 215, 287, 407, 527, 551,
7: 98, 175, 335, 671, 767, 1007, 1247, 1271,
8: 581, 869, 1241, 1349, 1541, 1769, 1829, 1961, 2021
MATHEMATICA
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}]
CROSSREFS
Cf. A238895.
Sequence in context: A136591 A277997 A009459 * A123055 A272306 A294996
KEYWORD
nonn,tabf
AUTHOR
T. D. Noe, Mar 28 2014
STATUS
approved