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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A064393 Exponent of highest power of 2 dividing n! equals the largest prime <= n. 2
4, 8, 9, 22, 26, 27, 32, 33, 50, 51, 56, 57, 70, 76, 77, 82, 94, 95, 100, 112, 118, 119, 128, 129, 134, 135, 176, 177, 186, 187, 196, 266, 267, 274, 275, 280, 296, 297, 342, 343, 352, 358, 364, 365, 372, 386, 387, 392, 393, 400, 406, 407, 426, 427, 454, 455 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

[n/2]+[n/4]+[n/8]+[n/16]+... = prevprime(n+1).

LINKS

Harvey P. Dale, Table of n, a(n) for n = 0..1000

EXAMPLE

4!=2^3*3, 8!=2^7*3^2*5*7, 9!=2^7*3^4*5*7, 22!=2^19*3^9*5^4*7^3*11^2*13*17*19.

MAPLE

for n from 3 to 10^3 do if sum(floor(n/(2^i)), i=1..15) = prevprime(n+1) then printf(`%d, `, n) fi; od:

MATHEMATICA

f[n_] := (t = 0; p = 2; While[s = Floor[n/p]; t = t + s; s > 0, p *= 2]; t); Do[ If[ f[n] == Prime[ PrimePi[n]], Print[n]], {n, 2, 500} ]

lp[n_]:=If[PrimeQ[n], n, NextPrime[n, -1]]; Select[Range[460], IntegerExponent[ #!, 2] == lp[#]&] (* Harvey P. Dale, Mar 02 2014 *)

CROSSREFS

Cf. A011371, A007917.

Sequence in context: A116030 A116020 A213015 * A173743 A035326 A180865

Adjacent sequences:  A064390 A064391 A064392 * A064394 A064395 A064396

KEYWORD

nonn

AUTHOR

Vladeta Jovovic, Sep 29 2001

EXTENSIONS

More terms from Robert G. Wilson v and James A. Sellers, Oct 01 2001

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 21 07:08 EDT 2019. Contains 327253 sequences. (Running on oeis4.)