A165930 a(1) = 1, for n > 1: a(n) = tau(sum of the previous terms) where tau(k) = number of the divisors of k.

1, 1, 2, 3, 2, 3, 6, 6, 8, 6, 4, 8, 6, 8, 7, 2, 2, 6, 5, 4, 12, 8, 8, 4, 4, 12, 8, 4, 12, 10, 6, 4, 8, 8, 12, 16, 4, 8, 8, 8, 4, 8, 8, 4, 4, 8, 8, 4, 4, 12, 8, 4, 16, 4, 12, 4, 8, 8, 4, 4, 16, 8, 12, 8, 8, 8, 18, 18, 12, 8, 8, 4, 8, 4, 8, 4, 4, 16, 4, 4, 16, 4, 8, 8, 8, 4, 8, 4, 24, 8, 4, 12, 8, 8, 4, 4, 16

Offset: 1

Author

Jaroslav Krizek, Sep 30 2009

Keywords

• nonn

Comments

a(1) = 1, for n > 1: a(n) = tau(sum_(i=1...n-1) a(i)) = A000005(sum_(i=1...n-1) a(i)). a(n) = inverse of partial sums of A064491(n), i.e. a(1) = A064491(1), for n > 1: a(n) = A064491(n) - A064491(n-1), i.e. first differences of sequence A064491.

Examples

			a(4) = tau(a(1)+a(2)+a(3)) = tau(4) = 3.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Programs

Haskell

a165930 n = a165930_list !! (n-1)
a165930_list = 1 : zipWith (-) (tail a064491_list) a064491_list
-- Reinhard Zumkeller, Mar 29 2014

PARI

print1(1);s=1;for(n=2,1e4,a=numdiv(s);print1(","a);s+=a)

Extensions

Program and editing by Charles R Greathouse IV, Nov 02 2009