A081973 -id:A081973 - cp's OEIS frontend

A085865 a(1) = 2, a(n+1) = a(n)*{sigma(a(n))}, where sigma(n) is the sum of the divisors function.

2, 6, 72, 14040, 707616000, 2299654269739008000, 25353370781704805143366427867873280000, 3361021040447648920437074194752848938805829494939344230020451929790873600000

Offset: 1

Amarnath Murthy, Jul 06 2003

nonn

a(1) = 1, a(n+1) = a(n) + sigma(a(n)) gives A081973.

			a(3) = 72 and sigma(72)= 195, hence a(4) = 72*195 = 14040.

Cf. A064491, A081973, A085864.

for(n=1,9,if(n==1,a=2,a*=sigma(a)); print(a); )

More terms from Ray Chandler, Jul 16 2003

A165929 a(1) = 1; for n > 1, a(n) = sigma(sum of the previous terms) where sigma(k) = sum of the divisors of k.

Original entry on oeis.org

1, 1, 3, 6, 12, 24, 48, 120, 264, 480, 1104, 2064, 4128, 10752, 19320, 38328, 91992, 170016, 369600, 745560, 1854720, 3845760, 7765296, 14990520, 29910120, 59856720, 119710416, 298755600, 667297320, 1446528360, 4011171840

Offset: 1

Jaroslav Krizek, Sep 30 2009

nonn

a(1) = 1; for n > 1, a(n) = sigma(Sum_{i=1..n-1} a(i)) = A000203(Sum_{i=1..n-1} a(i)).

a(n) = inverse of partial sums of A081973(n), i.e., a(1) = A081973(1); for n > 1, a(n) = A081973(n) - A081973(n-1), i.e., first differences of A081973.

			a(4) = sigma(a(1) + a(2) + a(3)) = sigma(1+1+3) = sigma(5) = 6.

Module[{lst={1}},Do[AppendTo[lst,DivisorSigma[1,Total[lst]]],{40}]; lst] (* Harvey P. Dale, Sep 29 2012 *)

print1(1);s=1;for(i=1,100,k=sigma(s);print1(","k);s+=k)

Extension and program from Charles R Greathouse IV, Oct 12 2009

cp's OEIS Frontend

A085865 a(1) = 2, a(n+1) = a(n)*{sigma(a(n))}, where sigma(n) is the sum of the divisors function.

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