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A185952 Partial products of A002313, the primes that are 1 or 2 (mod 4). 5

%I

%S 2,10,130,2210,64090,2371330,97224530,5152900090,314326905490,

%T 22945864100770,2042181904968530,198091644781947410,

%U 20007256122976688410,2180790917404459036690,246429373666703871145970

%N Partial products of A002313, the primes that are 1 or 2 (mod 4).

%C Product of the first n primes which are natural primes which are not Gaussian primes. Product of the first n primes congruent to 1 or 2 modulo 4. Product of the first n primes of form x^2+y^2. Product of the first n primes p such that -1 is a square mod p. Factors of primorials (A002110) not divisible by natural primes which are also Gaussian primes.

%C Essentially twice A006278.

%H G. C. Greubel, <a href="/A185952/b185952.txt">Table of n, a(n) for n = 1..300</a>

%F a(n) = Product_{i=1..n} A002313(i) = 2 * Product_{i=1..n} {p in A000040 but p not in A002145} = Product_{i=1..n} {A000040 intersection A042963}.

%e a(10) = 2 * 5 * 13 * 17 * 29 * 37 * 41 * 53 * 61 * 73 = 22945864100770.

%t Rest@ FoldList[#1*#2 &, 1, Select[ Prime@ Range@ 30, Mod[#, 4] != 3 &]] (* _Robert G. Wilson v_ *)

%o (PARI) pp(v)=my(t=1); vector(#v,i,t*=v[i])

%o pp(select(n->n%4<3, primes(20))) \\ _Charles R Greathouse IV_, Apr 21 2015

%Y Cf. A000040, A002110, A002313, A042963, A103222.

%K nonn,easy

%O 1,1

%A _Jonathan Vos Post_, Feb 07 2011

%E Terms corrected by _Robert G. Wilson v_, Feb 11 2011

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Last modified May 12 04:27 EDT 2021. Contains 343810 sequences. (Running on oeis4.)