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 A133028 Even perfect numbers divided by 2. 19
 3, 14, 248, 4064, 16775168, 4294934528, 68719345664, 1152921504069976064, 1329227995784915872327346307976921088, 95780971304118053647396689042151819065498660774084608, 6582018229284824168619876730229361455111736159193471558891864064, 7237005577332262213973186563042994240786838745737417944533177174565599576064 (list; graph; refs; listen; history; text; internal format)
 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 n such that A000203(n) is divisible 24. - Ctibor O. Zizka, Jun 29 2009 LINKS Table of n, a(n) for n=1..12. Omar E. Pol, Determinacion geometrica de los numeros primos y perfectos. FORMULA a(n) = A000396(n)/2. - R. J. Mathar, Oct 23 2007 [Assuming there are no odd perfect numbers. - Jianing Song, Sep 17 2022] a(n) = 2^(A000043(n) - 2) * A000668(n). - Omar E. Pol, Mar 01 2008 a(n) = A032742(A000396(n)), assuming there are no odd perfect numbers. 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 *) CROSSREFS Cf. A028334. Perfect numbers: A000396. Cf. A000043, A000668. Cf. A018254, A018487, A032742, A133024, A133025, A135652, A135653, A135654, A135655. Cf. A134708, A135650. - Omar E. Pol, Jul 07 2009 Sequence in context: A081383 A351139 A001320 * A144985 A168590 A309028 Adjacent sequences: A133025 A133026 A133027 * A133029 A133030 A133031 KEYWORD easy,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

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Last modified June 20 11:48 EDT 2024. Contains 373527 sequences. (Running on oeis4.)