A358509 - OEIS

%I #35 Nov 30 2022 00:02:01

%S 0,1,4,4,4,4,13,13,13,22,22,31,22,31,31,31,22,31,31,31,31,31,49,49,40,

%T 40,49,67,58,58,58,76,58,76,85,85,85,85,94,85,85,94,103,103,85,94,103,

%U 112,103,112,130,130,94,121,112,112,121,103,103,121,112,121,121,139,121,148,121,157,157,157,157,175,157,157

%N Sum of decimal digits of (3^n - 1)/2 (A003462).

%C a(n) == 4 (mod 9) for n >= 2. - _Robert Israel_, Nov 21 2022

%H Michel Marcus, <a href="/A358509/b358509.txt">Table of n, a(n) for n = 0..5000</a>

%F a(n) = A007953(A003462(n)).

%e For n=5, (3^n - 1)/2 = 121 so that a(5) = 1+2+1 = 4.

%p seq(convert(convert((3^n-1)/2,base,10),`+`),n=0..100); # _Robert Israel_, Nov 21 2022

%t a[n_] := Total[IntegerDigits[(3^n - 1)/2]]; Array[a, 100, 0] (* _Amiram Eldar_, Nov 20 2022 *)

%o (PARI) a(n) = sumdigits((3^n - 1)/2); \\ _Michel Marcus_, Nov 20 2022

%o (Python)

%o def A358509(n): return sum(map(int,str((3**n-1)>>1))) # _Chai Wah Wu_, Nov 21 2022

%Y Cf. A003462, A007953, A017209.

%Y Cf. A004166 (of 3^n).

%K nonn,base,easy

%O 0,3

%A _Paul Curtz_, Nov 20 2022