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a(1) = 1; a(2) = 2; a(n) = sigma_a[n-2] (a[n-1]), n > 2, where sigma_k (n) denotes the sum of the k-th powers of the divisors of n.
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%I #2 Feb 11 2014 19:05:28

%S 1,2,3,10,1134,3520155193849864644872367756250

%N a(1) = 1; a(2) = 2; a(n) = sigma_a[n-2] (a[n-1]), n > 2, where sigma_k (n) denotes the sum of the k-th powers of the divisors of n.

%e a(4) = sigma_a(2) (a(3)) = sigma_2 (3) = 1^2 + 3^2 = 10.

%K nonn

%O 1,2

%A _Joseph L. Pe_, May 08 2002