A358509 Sum of decimal digits of (3^n - 1)/2 (A003462).

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

Offset: 0

Author

Paul Curtz, Nov 20 2022

Keywords

• nonn
• base
• easy

Comments

a(n) == 4 (mod 9) for n >= 2. - Robert Israel, Nov 21 2022

Examples

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

Links

• Michel Marcus, Table of n, a(n) for n = 0..5000

Crossrefs

Cf. A003462, A007953, A017209.

Cf. A004166 (of 3^n).

Programs

Maple

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

Mathematica

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

PARI

a(n) = sumdigits((3^n - 1)/2); \\ Michel Marcus, Nov 20 2022

Python

def A358509(n): return sum(map(int,str((3**n-1)>>1))) # Chai Wah Wu, Nov 21 2022

Formula

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