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 A179076 Number of primes of the form k^2 + 1 less than n. 0

%I

%S 0,0,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,

%T 3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,

%U 4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,5,5,5,5

%N Number of primes of the form k^2 + 1 less than n.

%C The first n such that a(n) = 5 is a(102). Records in a(n) are a(n) = A002496(n)+1. Hardy and Littlewood conjectured that, asymptotically, a(n) ~ c*(sqrt(n))/log n, where c ~ 1.3727.

%D Richard K. Guy, Unsolved Problems in Number Theory, 2nd Edn., Springer, 1994, A1, pp.4-5.

%e a(3) = 1 because the unique prime of the form k^2 + 1 less than 3 is 1^2 + 1 = 2. The smallest value of n to reach the next record is a(6) = 2 because a(18) = 2, the two primes of the form k^2 + 1 less than 6 are 2 and 2^2 + 1 = 5. The smallest value of n to reach the next record is a(18) = 3 because the three primes of the form k^2 + 1 less than 18 are 2, 5, and 4^2 + 1 = 17.

%Y Cf. A000040, A002496.

%K easy,nonn

%O 1,6

%A _Jonathan Vos Post_, Jun 28 2010

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Last modified January 29 05:09 EST 2022. Contains 350672 sequences. (Running on oeis4.)