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

1,3

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.

Links

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

Example

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

Prog

(PARI) print1(1); s=1; for(n=2, 1e4, a=numdiv(s); print1(", "a); s+=a)
(Haskell)
a165930 n = a165930_list !! (n-1)
a165930_list = 1 : zipWith (-) (tail a064491_list) a064491_list
-- Reinhard Zumkeller, Mar 29 2014

Crossrefs

Sequence in context: A085211 A085212 A079025 * A300500 A339132 A064895

Adjacent sequences: A165927 A165928 A165929 * A165931 A165932 A165933

Keyword

nonn

Author

Jaroslav Krizek, Sep 30 2009

Extensions

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

Status

approved