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

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, 6, 6, 6, 6, 6, 4, 4, 4, 6, 6, 4, 6, 6

Offset: 1

Author

Omar E. Pol, Apr 01 2008, corrected Apr 03 2008

Keywords

• base
• nonn
• less

Comments

Also, final digit of n-th superperfect number A019279(n), if there are no odd superperfect numbers.

Examples

			a(5)=6 because the 5th even superperfect number A061652(5) is 4096 and the final digit of 4096 is 6.
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.
.............................................................
............... SHORT TABLE OF FINAL DIGITS .................
.............................................................
Final digit of ..... Final digit of Even ..... Final digit of
Mersenne prime ..... Superperfect number ..... Perfect number
A000668 ............ A061652 ................. A000396........
(3) ................ (2) ..................... (6) ........... (For n=1, only)
(7) ................ (4) ..................... (8) ...........
(1) ................ (6) ..................... (6) ...........
		

Links

• Landon Curt Noll, Mersenne Prime Digits.

Crossrefs

Cf. A000030, A000396, A000668, A077648, A019279, A061652, A135613, A135617, A138125.

Programs

Mathematica

Mod[#,10]&/@(2^(MersennePrimeExponent[Range[47]]-1)) (* Harvey P. Dale, Feb 23 2023 *)

Formula

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.

Extensions

a(40)-a(47) from Jinyuan Wang, Mar 14 2020