A289053 Array T(i,k) read by antidiagonals: position of prime(i)*prime(k) in A001358.

1, 3, 2, 9, 6, 4, 17, 13, 7, 5, 40, 26, 19, 11, 8, 56, 48, 31, 23, 15, 10, 90, 75, 61, 39, 28, 18, 12, 114, 103, 79, 68, 44, 34, 20, 14, 164, 135, 122, 94, 81, 54, 37, 24, 16, 253, 199, 172, 152, 118, 101, 65, 49, 30, 21

Offset: 1

Author

Zak Seidov, Jun 23 2017

Keywords

• nonn
• tabl

Examples

			Array begins:
    1      2      4      5      8     10    12    14    16    21
    3      6      7     11     15     18    20    24    30
    9     13     19     23     28     34    37    49
   17     26     31     39     44     54    65
   40     48     61     68     81    101
   56     75     79     94    118
   90    103    122    152
  114    135    172
  164    199
  253
		

Crossrefs

Cf. A000040, A001358, A115392 (1st row), A128301 (1st column).

Programs

Mathematica

With[{nn = 11}, Function[s, Table[Position[s, Prime[i] Prime[k]][[1, 1]], {i, nn}, {k, i, 1, -1}] // Flatten]@ Select[Range[Prime[nn]^2], PrimeOmega@ # == 2 &]] (* Michael De Vlieger, Jun 23 2017 *)