A131610 - OEIS

%I #7 Oct 13 2013 03:26:09

%S 25,33,39,58,93,123,134,146,155,177,185,253,278,295,358,362,417,446,

%T 478,538,566,597,614,698,749,766,794,898,917,982,998,1042,1059,1081,

%U 1149,1159,1286,1351,1393,1441,1546,1589,1623,1639,1649,1658,1718,1766,1799

%N Semiprimes that are the sum of three successive semiprimes.

%C 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.

%H Zak Seidov, <a href="/A131610/b131610.txt">Table of n,a(n) for n=1..10000</a>.

%F a(n)=A001358(m)=A001358(i)+A001358(i+1)+A001358(i+2), for some m, i.

%e 25=6+9+10, or A001358(9)=A001358(2)+A001358(3)+A001358(4),

%e 33=9+10+14, or A001358(11)=A001358(3)+A001358(4)+A001358(5).

%o (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

%Y Cf. A001358, A092192.

%K nonn

%O 1,1

%A _Zak Seidov_, Oct 02 2007