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A173891
Numbers n such that the n-th noncomposite number plus the (n+2)nd noncomposite number is an even semiprime.
1
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
1,2
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
FORMULA
prime(a(n+1)-1) = n-th balanced prime.
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
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
All but one value shifted by 1, and missing values (40, 634, 762) inserted, by R. J. Mathar, Apr 25 2010
STATUS
approved