

A083847


a(n) = number of primes of the form x^2 + 1 <= 2^n.


4



1, 1, 2, 2, 3, 4, 5, 6, 8, 10, 12, 14, 18, 24, 33, 42, 54, 70, 91, 114, 158, 212, 293, 393, 539, 713, 957, 1301, 1792, 2459, 3378, 4615, 6233, 8418, 11540, 15867, 21729, 29843, 41169, 56534, 77697, 106787, 147067, 203025, 280340, 387308, 535153, 739671, 1023655, 1416635, 1960813, 2716922, 3764693, 5218926, 7238715
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OFFSET

1,3


COMMENTS

It is conjectured that the number of primes of the form x^2+1 is infinite and thus this sequence does not become a constant, but this has never been proved.


REFERENCES

G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, 5th ed., Oxford Univ. Press, 1979, th. 17.
P. Ribenboim, The Little Book of Big Primes. SpringerVerlag, 1991, p. 190.


LINKS

Table of n, a(n) for n=1..55.
C. K. Caldwell, An amazing prime heuristic.
Eric Weisstein's World of Mathematics, Landau's Problems.


PROG

(PARI) a(n) = my(nb = 0); forprime(p=2, 2^n, if (issquare(p1), nb++); ); nb \\ Michel Marcus, Jun 14 2013


CROSSREFS

Cf. A005574, A002496, A083844  A083849.
Sequence in context: A055002 A114097 A174246 * A034142 A008675 A027581
Adjacent sequences: A083844 A083845 A083846 * A083848 A083849 A083850


KEYWORD

nonn


AUTHOR

Harry J. Smith, May 05 2003


EXTENSIONS

More terms from Alex Healy, Feb 06 2005


STATUS

approved



