A064517 Numbers k such that pi(k) is a square.

1, 2, 7, 8, 9, 10, 23, 24, 25, 26, 27, 28, 53, 54, 55, 56, 57, 58, 97, 98, 99, 100, 151, 152, 153, 154, 155, 156, 227, 228, 311, 312, 419, 420, 541, 542, 543, 544, 545, 546, 661, 662, 663, 664, 665, 666, 667, 668, 669, 670, 671, 672, 827, 828, 1009, 1010, 1011

Offset: 1

Author

Jason Earls, Oct 07 2001

Keywords

• easy
• nonn

Links

• Harry J. Smith, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000720.

Programs

PARI

pi(x, c=0) = forprime(p=2,x,c++); c for(n=1,2000, if(issquare(pi(n)),print1(n," ")))

PARI

{ n=0; for (m=1, 10^9, if (issquare(primepi(m)), write("b064517.txt", n++, " ", m); if (n==1000, break)) ) } \\ Harry J. Smith, Sep 17 2009