2,1

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.

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

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

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}]

Cf. A238895.

Sequence in context: A136591 A277997 A009459 * A123055 A272306 A294996

Adjacent sequences: A239622 A239623 A239624 * A239626 A239627 A239628

nonn,tabf

T. D. Noe, Mar 28 2014

approved