A365448 Array read by antidiagonals: row 1 is the semiprimes A001358; for m > 1, row m is the semiprimes that are the sum of two successive terms of row m-1.

4, 6, 10, 9, 15, 25, 10, 51, 146, 422, 14, 69, 201, 551, 973, 15, 77, 221, 667, 1858, 2831, 21, 85, 249, 1191, 89855, 312493, 127418369, 22, 95, 302, 1343, 110099, 2676567, 154171217

Offset

1,1

Links

Table of n, a(n) for n=1..35.

Example

The first 7 rows are
4, 6, 9, 10, 14, 15, 21, 22, 25, 26, ...
10, 15, 51, 69, 77, 85, 95, 106, 115, 134, ...
25, 146, 201, 221, 249, 302, 365, 529, 662, 681, ...
422, 551, 667, 1191, 1343, 2661, 6621, 11207, 13637, 14183, ...
973, 1858, 89855, 110099, 202394, 332377, 352147, 383507, 469231, 528923, ...
2831, 312493, 2676567, 3754285, 4027807, 9438362, 10568289, 20372991, 20590454, 21591014, ...
127418369, 154171217, 213938227, 242408953, 296917233, 325907227, 345235903, 367725381, ...
T(4,3) = 667 is a term because 667 = 23 * 29 is a semiprime and 667 = 392 + 365 where 302 = T(3,6) and 365 = T(3,7).

Maple

R[1]:= select(t -> numtheory:-bigomega(t) = 2, [$1..5*10^6]): M[1]:= nops(R[1]):
for i from 2 do
  R[i]:= select(t -> numtheory:-bigomega(t) = 2, R[i-1][1..M[i-1]-1] + R[i-1][2..M[i-1]]);
  M[i]:= nops(R[i]);
  if M[i] = 0 then break fi
od:
L:= NULL:
for k from 2 to 8 do
  L:= L, seq(R[i][k-i], i=1..k-1)
od:
L;

Crossrefs

Cf. A001358 (first row), A092192 (second row), A366167 (third row).

Sequence in context: A292767 A117622 A188673 * A193951 A129854 A088682

Adjacent sequences: A365445 A365446 A365447 * A365449 A365450 A365451

Keyword

nonn,tabl,more

Author

Zak Seidov and Robert Israel, Oct 03 2023

Status

approved