cp's OEIS Frontend

A138125 Final digit of n-th even superperfect number A061652(n).

%I A138125 #12 Feb 23 2023 11:41:12
%S A138125 2,4,6,4,6,6,4,4,6,6,4,4,6,4,4,4,6,6,6,4,6,6,6,6,6,6,6,4,4,6,4,4,6,4,
%T A138125 6,6,6,6,6,4,4,4,6,6,4,6,6
%N A138125 Final digit of n-th even superperfect number A061652(n).
%C A138125 Also, final digit of n-th superperfect number A019279(n), if there are no odd superperfect numbers.
%H A138125 Landon Curt Noll, <a href="http://www.isthe.com/chongo/tech/math/prime/mersenne.html">Mersenne Prime Digits</a>.
%F A138125 a(1)=2. For n>1, if final digit of n-th Mersenne prime A000668(n) is equal to 1 then a(n)=6, otherwise a(n)=4.
%e A138125 a(5)=6 because the 5th even superperfect number A061652(5) is 4096 and the final digit of 4096 is 6.
%e A138125 a(34)=4 because the final digit of 34th Mersenne prime is 7. a(39)=6 because the final digit of 39th Mersenne prime is 1.
%e A138125 .............................................................
%e A138125 ............... SHORT TABLE OF FINAL DIGITS .................
%e A138125 .............................................................
%e A138125 Final digit of ..... Final digit of Even ..... Final digit of
%e A138125 Mersenne prime ..... Superperfect number ..... Perfect number
%e A138125 A000668 ............ A061652 ................. A000396........
%e A138125 (3) ................ (2) ..................... (6) ........... (For n=1, only)
%e A138125 (7) ................ (4) ..................... (8) ...........
%e A138125 (1) ................ (6) ..................... (6) ...........
%t A138125 Mod[#,10]&/@(2^(MersennePrimeExponent[Range[47]]-1)) (* _Harvey P. Dale_, Feb 23 2023 *)
%Y A138125 Cf. A000030, A000396, A000668, A077648, A019279, A061652, A135613, A135617, A138125.
%K A138125 base,nonn,less
%O A138125 1,1
%A A138125 _Omar E. Pol_, Apr 01 2008, corrected Apr 03 2008
%E A138125 a(40)-a(47) from _Jinyuan Wang_, Mar 14 2020