A131610 Semiprimes that are the sum of three successive semiprimes.

25, 33, 39, 58, 93, 123, 134, 146, 155, 177, 185, 253, 278, 295, 358, 362, 417, 446, 478, 538, 566, 597, 614, 698, 749, 766, 794, 898, 917, 982, 998, 1042, 1059, 1081, 1149, 1159, 1286, 1351, 1393, 1441, 1546, 1589, 1623, 1639, 1649, 1658, 1718, 1766, 1799

Offset

1,1

Comments

a(n) = A001358(m) = A001358(i)+A001358(i+1)+A001358(i+2), for some m, i. Corresponding values of m and i are: 9, 11, 15, 21, 32, 42, 45, 50, 51, 57, 60, 81, 88, 92, 113, 115, 132, 137, 147, 168, 178, 186, 188; 2, 3, 4, 6, 10, 14, 15, 16, 17, 20, 21, 27, 31, 33, 38, 39, 45, 49, 52, 57, 60, 62, 65.

Links

Zak Seidov, Table of n,a(n) for n=1..10000.

Example

25=6+9+10, or A001358(9)=A001358(2)+A001358(3)+A001358(4),
33=9+10+14, or A001358(11)=A001358(3)+A001358(4)+A001358(5).

Mathematica

sp=Select[Range[612], PrimeOmega[#]==2&]; L=Length[sp]; s={}; Do[sm=sp[[n]]+sp[[n+1]]+sp[[n+2]]; If[PrimeOmega[sm]==2, AppendTo[s, sm]], {n, L-2}]; s (* James C. McMahon, Feb 26 2025 *)

Prog

(PARI) lista(nn) = {vec = vector(nn, i, i); sp = select(i->(bigomega(i) == 2), vec); for (i = 2, #sp-1, sumt = sp[i-1] + sp[i] + sp[i+1]; if (bigomega(sumt) == 2, print1(sumt, ", ")); ); } \\ Michel Marcus, Oct 13 2013

Crossrefs

Cf. A001358, A092192.

Sequence in context: A107608 A219951 A209333 * A211466 A269345 A134099

Adjacent sequences: A131607 A131608 A131609 * A131611 A131612 A131613

Keyword

nonn

Author

Zak Seidov, Oct 02 2007

Status

approved