A094540 Last digit of the n-th perfect number.

6, 8, 6, 8, 6, 6, 8, 8, 6, 6, 8, 8, 6, 8, 8, 8, 6

Offset

1,1

Comments

Conjecture: Ratio of 6's to 8's approaches 1.5 as a limit as this sequence approaches infinity. - J. Lowell, Jun 26 2007

Since the best known lower bound for odd perfect numbers is ca. 10^1500, I removed all terms after a(17). - Ivan Panchenko, Sep 16 2014

Links

Table of n, a(n) for n=1..17.

Math Forum at Drexel, List of Perfect Numbers

Eric Weisstein's World of Mathematics, Perfect Number

Maple

# (Maple code from N. J. A. Sloane)
# let s1 := list of terms in A000043
f:=n->if n mod 4 = 0 then 4 else n mod 4; fi; g:= x->2^f(x-1)*(2^f(x)-1); map(g, s1);

Mathematica

p={ the list of the Mersenne exponents (A000043) }; Mod[(PowerMod[2, p, 10] - 1)(PowerMod[2, p - 1, 10]), 10] (* Robert G. Wilson v, May 23 2004 *)

Crossrefs

Cf. A000396. See A000043 for the present state of knowledge about Mersenne primes.

Sequence in context: A200326 A088751 A153627 * A010724 A196822 A065356

Adjacent sequences: A094537 A094538 A094539 * A094541 A094542 A094543

Keyword

nonn,hard,base

Author

Eric W. Weisstein, May 08 2004

Extensions

Edited by N. J. A. Sloane, Apr 01 2008, at the suggestion of Ant King and Omar E. Pol

Status

approved