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A185952
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Partial products of A002313, the primes that are 1 or 2 (mod 4).
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5
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2, 10, 130, 2210, 64090, 2371330, 97224530, 5152900090, 314326905490, 22945864100770, 2042181904968530, 198091644781947410, 20007256122976688410, 2180790917404459036690, 246429373666703871145970
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OFFSET
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1,1
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COMMENTS
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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.
Essentially twice A006278.
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LINKS
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G. C. Greubel, Table of n, a(n) for n = 1..300
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FORMULA
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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}.
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EXAMPLE
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a(10) = 2 * 5 * 13 * 17 * 29 * 37 * 41 * 53 * 61 * 73 = 22945864100770.
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MATHEMATICA
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Rest@ FoldList[#1*#2 &, 1, Select[ Prime@ Range@ 30, Mod[#, 4] != 3 &]] (* Robert G. Wilson v *)
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PROG
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(PARI) pp(v)=my(t=1); vector(#v, i, t*=v[i])
pp(select(n->n%4<3, primes(20))) \\ Charles R Greathouse IV, Apr 21 2015
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CROSSREFS
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Cf. A000040, A002110, A002313, A042963, A103222.
Sequence in context: A305028 A119191 A125993 * A258971 A011805 A294350
Adjacent sequences: A185949 A185950 A185951 * A185953 A185954 A185955
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KEYWORD
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nonn,easy
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AUTHOR
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Jonathan Vos Post, Feb 07 2011
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EXTENSIONS
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Terms corrected by Robert G. Wilson v, Feb 11 2011
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STATUS
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approved
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