OFFSET
1,1
COMMENTS
a(13) has 314 digits and is too large to include. - R. J. Mathar, Oct 23 2007
Largest proper divisor of n-th even perfect number.
Also numbers k such that A000203(k) is divisible 24. - Ctibor O. Zizka, Jun 29 2009
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..15
FORMULA
a(n) = A000396(n)/2. - R. J. Mathar, Oct 23 2007 [Assuming there are no odd perfect numbers. - Jianing Song, Sep 17 2022]
MAPLE
a:=proc(n) if isprime(2^n-1)=true then 2^(n-2)*(2^n-1) else end if end proc: seq(a(n), n=1..120); # Emeric Deutsch, Oct 24 2007
MATHEMATICA
p = Select[2^Range[400] - 1, PrimeQ]; p*(p+1)/4 (* Vladimir Joseph Stephan Orlovsky, Feb 02 2012 *)
Map[2^(#-2) * (2^# - 1) &, MersennePrimeExponent[Range[12]]] (* Amiram Eldar, Oct 21 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Oct 20 2007, Apr 23 2008, Apr 28 2009
EXTENSIONS
More terms from R. J. Mathar and Emeric Deutsch, Oct 23 2007
STATUS
approved