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%I #18 Oct 13 2014 04:19:55
%S 2,6,26,94,314,986,3160,9990,31614,99996,316206,999960,3162246,
%T 9999960,31622764,99999966,316227734,999999924,3162277654,9999999956,
%U 31622776500,99999999964,316227766006,999999999886,3162277660140
%N a(n)^2 + 1 is largest prime of the form x^2 + 1 <= 10^n.
%C It is conjectured that the number of primes of the form x^2+1 is infinite and thus this sequence never becomes a constant, but this has not been proved.
%C The ratio a(n+2)/a(n) appears to approach 10, as one might expect. - _Bill McEachen_, Nov 03 2013
%D G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, 5th ed., Oxford Univ. Press, 1979, th. 17.
%D P. Ribenboim, The Little Book of Big Primes. Springer-Verlag, 1991, p. 190.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/LandausProblems.html">Landau's Problems.</a>
%t Do[ k = Floor[ Sqrt[ 10^n] - 1]; While[ !PrimeQ[k^2 + 1], k-- ]; Print[k], {n, 1, 25}]
%Y Cf. A005574, A002496, A083844, A083846, A083847, A083848, A083849.
%K nonn
%O 1,1
%A _Harry J. Smith_, May 05 2003
%E Edited and extended by _Robert G. Wilson v_, May 08 2003