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

Author

Zak Seidov, Oct 02 2007

Keywords

• nonn

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.

Examples

			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).
		

Links

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

Crossrefs

Cf. A001358, A092192.

Programs

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 *)

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