A176512 Indices of products of 2 single (or isolated or non-twin) primes in the semiprimes.

1, 16, 25, 33, 35, 45, 52, 55, 58, 62, 76, 82, 84, 100, 104, 107, 111, 133, 137, 143, 155, 158, 162, 164, 174, 183, 188, 194, 198, 202, 214, 218, 222, 225, 229, 231, 234, 241, 243, 249, 257, 263, 265, 269, 274, 281, 287, 292, 294, 299, 301, 304, 319, 320, 321

Offset: 1

Author

Juri-Stepan Gerasimov, Apr 19 2010

Keywords

• nonn

Programs

Maple

From R. J. Mathar, May 02 2010: (Start)
isA007510 := proc(n) isprime(n) and not isprime(n+2) and not isprime(n-2) ; simplify(%) ; end proc:
isA176312 := proc(n) for d in numtheory[divisors](n) do if isA007510(d) and isA007510(n/d) then return true; end if; end do: return false; end proc:
A176312 := proc(n) option remember; if n = 1 then 4; else for a from procname(n-1)+1 do if isA176312(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:
A176512 := proc(n) A174956(A176312(n)) ; end proc:
seq(A176512(n),n=1..120) ; (End)

Formula

A001358(k) = A176312(a(n)).

a(n) = A174956(A176312(n)). - R. J. Mathar, May 02 2010

Extensions

Entries checked by R. J. Mathar, May 02 2010