A135617 - OEIS

%I #47 Oct 16 2024 09:19:58

%S 6,2,4,8,3,8,1,2,2,1,1,1,2,1,5,1,9,3,1,4,1,5,3,9,1,8,3,1,1,1,2,1,8,8,

%T 3,1,8,9,4,7,4,7,4,7,2,1,5,1

%N a(n) is the initial digit of n-th even perfect number.

%C a(n) is also the initial digit of n-th perfect number A000396(n) if there are no odd perfect numbers.

%H Omar E. Pol, <a href="http://www.polprimos.com/#Los%20n%C3%BAmeros%20perfectos">Los números perfectos</a>, (in Spanish).

%e a(5) = 3 because the 5th even perfect number is 33550336 and the initial digit of 33550336 is 3.

%t lst = {* the list of terms in A000043 *}; f[n_] := Block[{pn = (2^n - 1) (2^(n - 1))}, Quotient[pn, 10^Floor[ Log[10, pn]] ]]; f@# & /@ lst (* _Robert G. Wilson v_, Apr 01 2008 *)

%Y Cf. A000030, A000396, A077648, A094540, A133033.

%K nonn,base,more

%O 1,1

%A _Omar E. Pol_, Mar 01 2008

%E More terms from _Robert G. Wilson v_, Apr 01 2008

%E Definition clarified by _Omar E. Pol_, Apr 14 2018

%E a(40)-a(47) from _Ivan Panchenko_, Apr 16 2018

%E a(48) from _Amiram Eldar_, Oct 16 2024