A078586 a(n) is the product of the first n primes of the form 4k+3.

3, 21, 231, 4389, 100947, 3129357, 134562351, 6324430497, 373141399323, 25000473754641, 1775033636579511, 140227657289781369, 11638895555051853627, 1198806242170340923581, 128272267912226478823167, 16290578024852762810542209, 2134065721255711928181029379

Offset

1,1

Comments

a(n)+2 is a prime for n=1,2,3,4,8,10,12,17,19,22,23,53.

Product of first n primes that are also Gaussian primes; product of first n primes that are not of the form x^2+y^2.

Links

T. D. Noe, Table of n, a(n) for n = 1..100

Mathematica

maxN=15; pLst={}; k=0; While[Length[pLst]<maxN, k++; If[PrimeQ[4k-1], AppendTo[pLst, 4k-1]]]; lst=Drop[FoldList[Times, 1, pLst], 1]

Prog

(PARI) a(n)=my(t=1); forprime(p=2, , if(p%4==3, t*=p; if(n--<1, return(t)))) \\ Charles R Greathouse IV, Mar 09 2014

Crossrefs

Cf. A002110, A006278, A038347.

Sequence in context: A326604 A008545 A005373 * A179331 A138903 A375898

Adjacent sequences: A078583 A078584 A078585 * A078587 A078588 A078589

Keyword

easy,nonn

Author

T. D. Noe, Dec 01 2002

Status

approved