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A366662
Sum of the divisors of 9^n-1.
12
15, 186, 1680, 15876, 123690, 1541568, 8992680, 111757968, 967814400, 9366647892, 62424587520, 852903426816, 4766016364260, 55176998178240, 550081165885440, 4829754617483040, 31725040326819840, 471309320999516160, 2535353780263288800, 33995669076586206864
OFFSET
1,1
LINKS
FORMULA
a(n) = sigma(9^n-1) = A000203(A024101(n)).
a(n) = A366576(2*n) = A366576(n) * A366578(n) * (2^(4 + A007814(n)) - 1) / (2^(3 + A007814(n)) - 1) / 3. - Max Alekseyev, Jan 07 2024
EXAMPLE
a(2)=186 because 9^2-1 has divisors {1, 2, 4, 5, 8, 10, 16, 20, 40, 80}.
MAPLE
a:=n->numtheory[sigma](9^n-1):
seq(a(n), n=1..30);
MATHEMATICA
DivisorSigma[1, 9^Range[30]-1]
KEYWORD
nonn
AUTHOR
Sean A. Irvine, Oct 15 2023
STATUS
approved