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A340468
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a(n) is the least prime of the form 2 + Product_{i=n..m} prime(i).
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1
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5, 7, 79, 13, 223, 19, 439, 130753887906569681111538991218568790437537693430279000532630035672131604633987039552816424896353327834998483765849409837393409377729040653460715050958787058270805333463, 31, 34826927179023475480751694965449235272424989980919
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OFFSET
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2,1
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COMMENTS
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If n is in A029707, a(n) = 2+prime(n).
If n is not in A029707 but prime(n) is in A051507, a(n) = 2+prime(n)*prime(n+1).
a(15) > 10^1000 if it exists.
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LINKS
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EXAMPLE
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a(2) = 2+3 = 5.
a(3) = 2+5 = 7.
a(4) = 2+7*11 = 79.
a(5) = 2+11 = 13.
a(6) = 2+13*17 = 223.
a(7) = 2+17 = 19.
a(8) = 2+19*23 = 439.
a(9) = 2+23*29*...*431.
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MAPLE
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f:= proc(n) local i, t;
t:= 1;
for i from n do
t:= t*ithprime(i);
if isprime(t+2) then return t+2 fi;
od
end proc:
seq(f(n), n=2..14);
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PROG
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(Python)
from sympy import isprime, nextprime, prime
def a(n):
prodpnpm = pm = prime(n)
while not isprime(2+prodpnpm): pm = nextprime(pm); prodpnpm *= pm
return 2+prodpnpm
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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