login
Indices of products of 2 single (or isolated or non-twin) primes in the semiprimes.
1

%I #5 Feb 06 2019 23:39:03

%S 1,16,25,33,35,45,52,55,58,62,76,82,84,100,104,107,111,133,137,143,

%T 155,158,162,164,174,183,188,194,198,202,214,218,222,225,229,231,234,

%U 241,243,249,257,263,265,269,274,281,287,292,294,299,301,304,319,320,321

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

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

%F a(n) = A174956(A176312(n)). - _R. J. Mathar_, May 02 2010

%p From _R. J. Mathar_, May 02 2010: (Start)

%p isA007510 := proc(n) isprime(n) and not isprime(n+2) and not isprime(n-2) ; simplify(%) ; end proc:

%p 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:

%p 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:

%p 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:

%p A176512 := proc(n) A174956(A176312(n)) ; end proc:

%p seq(A176512(n),n=1..120) ; (End)

%K nonn

%O 1,2

%A _Juri-Stepan Gerasimov_, Apr 19 2010

%E Entries checked by _R. J. Mathar_, May 02 2010