A176807 Lesser of twin primes p such that p = semiprime(k)/3 and p + 2 = semiprime(k+3)/3 for some integer k.
3, 107, 137, 179, 239, 419, 461, 659, 1049, 1091, 1697, 1787, 1871, 2027, 2111, 2381, 2687, 2711, 3167, 3299, 3329, 3359, 3371, 3467, 3851, 4259, 4721, 4967, 5279, 5501, 5639, 5651, 5867, 6269, 6449, 7487, 8819, 8969, 9011, 9431, 9629
Offset: 1
Keywords
Examples
3 is a term because 3 = semiprime(3)/3 = 9/3 and 3 + 2 = 5 = semiprime(3+3)/3 = 15/3.
Programs
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Maple
From R. J. Mathar, Apr 27 2010: (Start) isA001358 := proc(n) numtheory[bigomega](n) = 2 ; end proc: A001358 := proc(n) option remember ; if n = 1 then 4; else for a from procname(n-1)+1 do if isA001358(a) then return a; end if; end do: end if ; end proc: A174956 := proc(p) option remember ; for n from 1 do if A001358(n) = p then return n; elif A001358(n) > p then return 0 ; end if; end do: end proc: A001359 := proc(n) option remember; if n = 1 then 3; else for a from procname(n-1)+2 by 2 do if isprime(a) and isprime(a+2) then return a; end if; end do: end if; end proc: for i from 1 to 200 do p := A001359(i) ; n := A174956(3*p) ; n3 := A174956(3*p+6) ; if n > 0 and n3 >0 and n3=n+3 then printf("%d,",p) ; end if; end do: (End)
Extensions
Corrected (659 inserted, 1031 removed, 2027 inserted) and extended by R. J. Mathar, Apr 27 2010