1,1

Also, concatenation of final digit of n-th superperfect number A019279(n), final digit of n-th Mersenne prime A000668(n) and final digit of n-th perfect number A000396(n), if there are no odd superperfect numbers.

Also, concatenation of A138125(n), A080172(n) and A094540(n).

For n>1 a(n) is equal to 478 or 616, only.

Note that, for n>1: if the final digit of n-th Mersenne prime A000668(n) is 1 then the final digit of n-th even superperfect number is 6 and the final digit of n-th perfect number also is 6, otherwise the final digit of n-th even superperfect number is 4 and the final digit of n-th perfect number is 8 (See example).

L. C. Noll, Mersenne Prime Digits and Names".

J. M. Pedersen, Known Perfect Numbers.

O. E. Pol, Determinacion geometrica de los numeros primos y perfectos".

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.................. SHORT TABLE OF FINAL DIGITS ...................

===================================================================

... Final digit of even ..... Final digit of ..... Final digit of

... superperfect number ..... Mersenne prime ..... perfect number

........ A061652 ............... A000668 ............. A000396

===================================================================

n = 1 ..... (2) ................... (3) .................. (6)

n > 1 ..... (4) ................... (7) .................. (8)

n > 1 ..... (6) ................... (1) .................. (6)

Cf. A000396, A000668, A019279, A061652, A080172, A094540, A138125, A138816, A138817, A138818, A138841, A138842, A138843.

Sequence in context: A146092 A146126 A138818 this_sequence A138820 A005391 A036270

Adjacent sequences: A138816 A138817 A138818 this_sequence A138820 A138821 A138822

base,nonn

Omar E. Pol (info(AT)polprimos.com), Apr 05 2008