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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 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

T. D. Noe, Rows n = 2..51 of irregular triangle, flattened

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

Adjacent sequences:  A239622 A239623 A239624 * A239626 A239627 A239628

KEYWORD

nonn,tabf

AUTHOR

T. D. Noe, Mar 28 2014

STATUS

approved

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Last modified November 18 02:07 EST 2019. Contains 329242 sequences. (Running on oeis4.)