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A354456
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a(n) is the least number k such that k - 5^i is prime for i = 1..n.
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0
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7, 28, 132, 666, 3234, 17514, 100674, 501228, 2062662, 211097334, 2597411082, 34473310284, 214852200444, 394471192794
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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a(3) = 132 because 132 - 5^1 = 127, 132 - 5^2 = 107 and 132 - 5^3 = 7 are all prime, and 132 is the least number with this property.
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MAPLE
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g:= proc(n) local p, x, i;
p:= 1:
do
p:= nextprime(p);
x:= p + 5^n;
if andmap(isprime, [seq(x-5^i, i=1..n-1)]) then return x fi
od
end proc:
map(g, [$1..10]);
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PROG
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(Python)
from sympy import isprime, nextprime
def a(n):
p = 2
while True:
k, p = 5**n + p, nextprime(p)
if all(isprime(k-5**i) for i in range(1, n)):
return k
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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