login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A219097 Parity of pi(2^n). 4
0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0

COMMENTS

The parity of pi(n) is obtained without calculating pi(n), and much more quickly. See the paper below.

LINKS

Table of n, a(n) for n=0..90.

Henri Lifchitz, Parity of pi(n)

EXAMPLE

For n = 5 , pi(2^5) = 11 = 1 (mod 2).

MAPLE

A071986 := proc(n)

    numtheory[pi](n) mod 2 ;

end proc:

A219097 := proc(n)

    A071986(2^n) ;

end proc: # R. J. Mathar, Nov 12 2012

MATHEMATICA

Table[Mod[PrimePi[2^n], 2], {n, 32}] (* Alonso del Arte, Nov 12 2012 *)

CROSSREFS

Cf. A071986, A131378, A006880, A219071.

Sequence in context: A238469 A189664 A260446 * A188294 A258021 A258998

Adjacent sequences:  A219094 A219095 A219096 * A219098 A219099 A219100

KEYWORD

nonn

AUTHOR

Henri Lifchitz, Nov 11 2012

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified March 28 22:27 EDT 2017. Contains 284249 sequences.