A173891 Numbers n such that the n-th noncomposite number plus the (n+2)nd noncomposite number is an even semiprime.

1, 3, 16, 37, 40, 47, 55, 56, 74, 103, 108, 111, 119, 130, 161, 165, 185, 188, 195, 200, 219, 240, 272, 273, 292, 340, 359, 388, 420, 427, 465, 466, 509, 521, 554, 600, 606, 622, 630, 634, 668, 683, 684, 703, 710, 711, 734, 762, 792, 814, 822, 823, 830, 831

Offset: 1

Author

Juri-Stepan Gerasimov, Mar 01 2010

Keywords

• nonn

Comments

Numbers n such that (A008578(n) + A008578(n+2))/2 is prime.

Is this the same as A173390? - R. J. Mathar, Jul 22 2010

Crossrefs

Cf. A006562, A008578, A100484.

Programs

Maple

A008578 := proc(n) if n = 1 then 1; else ithprime(n-1) ; end if; end proc: for n from 1 to 1000 do sp := A008578(n)+A008578(n+2) ; if type(sp,'even') and numtheory[bigomega](sp) = 2 then printf("%d,",n) ; end if; end do: # R. J. Mathar, Apr 25 2010

Formula

prime(a(n+1)-1) = n-th balanced prime.

Extensions

All but one value shifted by 1, and missing values (40, 634, 762) inserted, by R. J. Mathar, Apr 25 2010