This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A064523 Numbers n such that pi(n^2) is a square. 2
 1, 3, 5, 10, 2640, 8304, 11699, 15330, 16810, 16910, 22463, 25906, 26652, 35950, 72429, 75470, 134141, 142413, 194711, 270353, 296073, 371964, 496254, 654609, 1640679, 1729409, 1854680, 4434965, 4973898, 5584120, 5783816 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(28) > 2*10^6. [Donovan Johnson, May 30 2010] LINKS EXAMPLE n = 14: a(14) = 35950, Pi(35950^2) = Pi(1292402500) = 64866916 = 8054^2 MATHEMATICA Do[ If[ IntegerQ[ Sqrt[ PrimePi[n^2]]], Print[n]], {n, 1, 400000} ] lst = {}; Do[ If[ IntegerQ@ Sqrt@ PrimePi[n^2], AppendTo[lst, n]; Print@n], {n, 520000}]; lst (* Robert G. Wilson v, Feb 03 2006 *) PROG (PARI) pi(x, c=0) = forprime(p=2, x, c++); c for(n=1, 10^6, if(issquare(pi(n^2)), print1(n, " "))) CROSSREFS Cf. A000720, A115835 (square root of pi(a(n))). Sequence in context: A305510 A024329 A297422 * A268034 A286567 A258862 Adjacent sequences:  A064520 A064521 A064522 * A064524 A064525 A064526 KEYWORD nonn AUTHOR Jason Earls, Oct 07 2001 EXTENSIONS More terms from Robert G. Wilson v and Labos Elemer, Oct 08 2001 Further terms from Robert G. Wilson v, Oct 16 2001 a(20) from Robert G. Wilson v, Feb 03 2006 Added missing terms 134141, 142413, 194711 and a(24)-a(27) from Donovan Johnson, May 30 2010 a(28)-a(31) from Chai Wah Wu, Aug 27 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 17 22:53 EDT 2019. Contains 327147 sequences. (Running on oeis4.)