OFFSET
1,2
COMMENTS
Conjecture: column k lists also the numbers n having k pairs of equidistant subparts in the symmetric representation of sigma(n).
For more information about the "subparts" see A279387.
This sequence is a permutation of the natural numbers.
LINKS
EXAMPLE
The upper-left corner of the square array begins:
1, 3, 21, 75, 105, 315, 495, 945, 1575, 2835, ...
2, 5, 27, 135, 189, 525, 585, 1155, 2475, ...
4, 7, 33, 147, 225, 675, 765, 1365, ...
6, 9, 39, 165, 297, 693, 855, ...
8 10, 45, 171, 351, 735, ...
12, 11, 51, 175, 385, ...
16, 13, 55, 195, ...
20, 14, 57, ...
24, 15, ...
28, ...
...
MATHEMATICA
jMax = 11; nMax = 5000; cnt[n_] := cnt[n] = DivisorSum[n, Boole[OddQ[#] && # > Sqrt[2n]]&]; col[k_] := Select[Range[nMax], cnt[#] == k&]; T[j_, k_] := col[k][[j]]; Table[T[j-k, k], {j, 1, jMax}, {k, 0, j-1}] // Flatten (* Jean-François Alcover, Feb 16 2017 *)
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Omar E. Pol, Feb 15 2017
STATUS
approved