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A078443 Numbers which are both interprime and semiprime. 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

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

EXAMPLE

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

MATHEMATICA

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

PROG

(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

CROSSREFS

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

Sequence in context: A086697 A287568 A251728 * A085751 A263106 A116589

Adjacent sequences:  A078440 A078441 A078442 * A078444 A078445 A078446

KEYWORD

nonn

AUTHOR

Lior Manor Dec 31 2002

STATUS

approved

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Last modified October 14 12:45 EDT 2019. Contains 328006 sequences. (Running on oeis4.)