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A158288
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The number of twin prime pairs in the n-th century.
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1
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8, 7, 4, 2, 3, 2, 3, 0, 5, 0, 5, 1, 3, 2, 4, 0, 4, 2, 2, 3, 3, 3, 2, 3, 0, 2, 2, 3, 1, 1, 0, 2, 2, 4, 2, 4, 1, 1, 2, 2, 4, 2, 5, 1, 2, 2, 2, 2, 0, 2, 2, 0, 2, 0, 3, 2, 3, 1, 3, 0, 1, 2, 1, 1, 1, 2, 2, 4, 2, 2, 0, 1, 1, 3, 2, 3, 0, 1, 1, 1, 2, 0, 3, 1, 1, 2, 1, 0, 3, 1, 2, 0, 2, 1, 4, 0, 2, 2, 1, 1, 4, 1, 1, 2, 2
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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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FORMULA
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MAPLE
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f:= proc(n) local P;
P:= select(isprime, {seq(i, i=100*n-99..100*n-1, 2)});
nops(P intersect map(`+`, P, 2))
end proc:
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MATHEMATICA
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Table[Count[Prime@ Range[Boole[n == 1] + PrimePi[100 (n - 1) + 1], PrimePi[100 n] - 1], _?(PrimeQ[# + 2] &)], {n, 105}] (* Michael De Vlieger, Jul 20 2017 *)
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PROG
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(PARI) a(n)=my(s=0); forprime(p=100*n-99, 100*n-2, if(isprime(p+2), s++)); s \\ Charles R Greathouse IV, Feb 03 2011
(Python)
from sympy import primerange, isprime
def a(n):
s=0
for p in primerange(100*n - 99, 100*n - 1):
if isprime(p + 2):s+=1
return s
print([a(n) for n in range(1, 201)]) # Indranil Ghosh, Jul 20 2017, after PARI code
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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