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A131610 Semiprimes that are the sum of three successive semiprimes. 5
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 (list; graph; refs; listen; history; text; internal format)
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.

FORMULA

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

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).

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

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Last modified August 20 11:41 EDT 2017. Contains 290835 sequences.