

A109310


Numbers n such that difference between nth and (n+1)st semiprimes is a semiprime (sp).


0



4, 6, 18, 21, 23, 30, 36, 42, 43, 50, 68, 76, 78, 80, 87, 88, 91, 98, 108, 111, 116, 117, 118, 120, 127, 128, 134, 138, 141, 150, 151, 152, 153, 156, 164, 168, 171, 179, 185, 186, 192, 195, 196, 204, 212, 215, 216, 226, 232, 236, 237, 244, 245, 250, 255, 266
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OFFSET

1,1


LINKS

Table of n, a(n) for n=1..56.


EXAMPLE

4 is ok because sp(4)=10, sp(5)=14, 1410=sp(1), sp(n)=A001358(n)=nth semiprime.


PROG

(PARI) lista(nn) = {vec = vector(nn, i, i); sp = select(i>(bigomega(i)==2), vec); for (i = 1, #sp1, if (bigomega(sp[i+1]sp[i]) == 2, print1(i, ", ")); ); } \\ Michel Marcus, Oct 06 2013


CROSSREFS

Cf. A001358 = Semiprimes, A092191 = numbers n such that sum of nth and (n+1)st semiprimes is a semiprime.
Sequence in context: A062046 A102020 A125133 * A219190 A120391 A064217
Adjacent sequences: A109307 A109308 A109309 * A109311 A109312 A109313


KEYWORD

nonn


AUTHOR

Zak Seidov, Jun 27 2005


STATUS

approved



