This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A094540 #46 Feb 16 2025 08:32:53
%S A094540 6,8,6,8,6,6,8,8,6,6,8,8,6,8,8,8,6
%N A094540 Last digit of the n-th perfect number.
%C A094540 Conjecture: Ratio of 6's to 8's approaches 1.5 as a limit as this sequence approaches infinity. - _J. Lowell_, Jun 26 2007
%C A094540 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
%D A094540 David Wells, The Penguin Dictionary of Curious and Interesting Numbers. Penguin Books, NY, 1986, Revised edition 1987. See p. 107.
%H A094540 Math Forum at Drexel, <a href="https://web.archive.org/web/20171219230744/http://mathforum.org/library/drmath/view/51516.html">List of Perfect Numbers</a>.
%H A094540 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PerfectNumber.html">Perfect Number</a>.
%p A094540 # (Maple code from _N. J. A. Sloane_)
%p A094540 # let s1 := list of terms in A000043
%p A094540 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);
%t A094540 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 *)
%Y A094540 Cf. A000396. See A000043 for the present state of knowledge about Mersenne primes.
%K A094540 nonn,hard,base
%O A094540 1,1
%A A094540 _Eric W. Weisstein_, May 08 2004
%E A094540 Edited by _N. J. A. Sloane_, Apr 01 2008, at the suggestion of _Ant King_ and _Omar E. Pol_