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A305755 Odd semiprimes sandwiched by even semiprimes. 0
9, 25, 33, 35, 39, 77, 85, 95, 141, 155, 201, 259, 355, 361, 395, 481, 559, 565, 623, 763, 799, 841, 865, 879, 923, 933, 979, 1003, 1043, 1177, 1199, 1219, 1227, 1285, 1293, 1299, 1437, 1441, 1517, 1541, 1603, 1643, 1655, 1717, 1769, 1865, 2005, 2041, 2095, 2101, 2123, 2127, 2183, 2245 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Odd semiprimes sp(k) = A001358(k) such that sp(k-1) and sp(k+1) are even. Values of k: 3, 9, 11, 13, 15, 26, 28, 34, 46, 51, 63, 83, 112, 114, 125, 148, 175, 177, 190, 230, 242, 253, 259, 264, 278, 280, 293.

LINKS

Table of n, a(n) for n=1..54.

EXAMPLE

a(1) = 9: A001358(2) = 6, A001358(3) = 9, A001358(4) = 10;

a(2) = 25: A001358(8) = 22, A001358(9) = 25, A001358(10) = 26.

MATHEMATICA

s = Select[Range[2300], Plus @@ Last /@ FactorInteger[#] == 2 &]; Transpose[ Select[ Partition[s, 3, 1], Mod[#, 2] == {0, 1, 0} &]][[2]] (* Giovanni Resta, Jun 10 2018 *)

CROSSREFS

Cf. A001358.

Sequence in context: A326742 A246328 A065772 * A090333 A137190 A044070

Adjacent sequences:  A305752 A305753 A305754 * A305756 A305757 A305758

KEYWORD

nonn

AUTHOR

Zak Seidov, Jun 10 2018

STATUS

approved

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Last modified May 14 19:53 EDT 2021. Contains 343903 sequences. (Running on oeis4.)