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A090405
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a(n) = PrimePi(n+2) - PrimePi(n).
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3
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2, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 1
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OFFSET
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1,1
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COMMENTS
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For n>1, a(n) = 1 if n+1 or n+2 is prime, otherwise a(n) = 0. - Robert Israel, Mar 30 2017
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LINKS
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MAPLE
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MATHEMATICA
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Table[Subtract @@ Map[PrimePi, n + {2, 0}], {n, 120}] (* or *)
Table[Boole@ PrimeQ[n + 1 + Boole[OddQ@ n]] + Boole[n == 1], {n, 120}] (* Michael De Vlieger, Mar 30 2017 *)
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PROG
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(PARI) for(n=1, 100, print1(primepi(n + 2) - primepi(n), ", ")) \\ Indranil Ghosh, Mar 31 2017
(Python)
from sympy import primepi
print([primepi(n + 2) - primepi(n) for n in range(1, 101)])
(Python)
from sympy import isprime
def a(n):
if n<2: return 2
else:
if isprime(n + 1 + (n%2 == 1) + (n==1)): return 1
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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