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A230774
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Number of primes less than first prime above square root of n.
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2
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1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5
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OFFSET
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1,5
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COMMENTS
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Or repeat k (prime(k)^2 - prime(k-1)^2) times, with prime(0) set to 0 for k = 1.
This sequence is useful to compute A055399 for prime numbers.
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LINKS
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FORMULA
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Repeat 1 prime(1)^2 = 4 times; for k>1, repeat k (prime(k)^2-prime(k-1)^2) = A050216(k-1) times.
a(n) - A056811(n) = characteristic function of squares of primes.
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EXAMPLE
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a(5) = a(6) = a(7) = a(8) = a(9) = 2 because prime(1) = 2 < sqrt(5 to 9) <= prime(2) = 3.
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MATHEMATICA
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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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