This site is supported by donations to The OEIS Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A178911 Perfex numbers: n = binary XOR of divisors of n. 2
 1, 6, 120, 198, 3696, 6240, 32640, 56160, 1941408, 3592200, 8119800, 15628032, 27125280, 59032080, 61788240, 125859840, 1635834720, 2147450880, 3709081680, 16328199552, 26198072160, 52344970080, 52396088160 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(17) > 1e9. 10^11 < a(24) <= 209584184160. a(25) <= 210197601120. - Donovan Johnson, Mar 12 2011 LINKS MATHEMATICA lst = {}; k = 1; While[k < 10^9, If[ BitXor @@ Divisors@k == k, AppendTo[lst, k]; Print@k]; k++ ]; lst (* Robert G. Wilson v, Jun 27 2010 *) PROG (PARI) xigma(n)=local(ds, r); ds=divisors(n); for(k=1, #ds, r=bitxor(r, ds[k])); r for(n=1, 1000000000, if(xigma(n)==n, print1(n", "))) CROSSREFS Cf. A178910, A178909, A000396, A003987. Sequence in context: A246827 A127726 A117063 * A227027 A001219 A224303 Adjacent sequences:  A178908 A178909 A178910 * A178912 A178913 A178914 KEYWORD base,more,nonn AUTHOR Franklin T. Adams-Watters, Jun 22 2010 EXTENSIONS a(17) from Robert G. Wilson v, Jul 30 2010 a(18)-a(23) from Donovan Johnson, Mar 12 2011 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 January 17 10:56 EST 2019. Contains 319218 sequences. (Running on oeis4.)