A078443 Numbers which are both interprime and semiprime.

4, 6, 9, 15, 21, 26, 34, 39, 69, 86, 93, 111, 129, 134, 205, 217, 254, 274, 309, 334, 381, 386, 393, 446, 453, 473, 489, 501, 515, 566, 667, 687, 723, 771, 803, 879, 933, 939, 974, 1003, 1011, 1126, 1167, 1207, 1226, 1234, 1243, 1286, 1294, 1299, 1313, 1465

Offset: 1

Author

Lior Manor, Dec 31 2002

Keywords

• nonn

Comments

Ratio of the number of odd terms to the number of even terms increases with increasing n. - Zak Seidov, May 22 2015

Examples

			a[8]=39 because 39=(37+41)/2 and 39=3*13
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Intersection of A001358 and A024675. - Zak Seidov, May 22 2015

Programs

Mathematica

Select[Mean/@Partition[Prime[Range[250]],2,1],PrimeOmega[#]==2&] (* Harvey P. Dale, Oct 08 2013 *)

PARI

lista(nn) = {prevp = 2; forprime (p=3, nn, n = p + prevp; if (n % 2 == 0, if (bigomega(n/2) == 2, print1(n/2, ", "););); prevp = p;);} \\ Michel Marcus, Jun 09 2013