OFFSET
1,2
COMMENTS
Sum of all the products formed by multiplying together the number of divisors of each divisor of the numbers from 1 to n.
Partial sums of A211776. [Joerg Arndt, Feb 11 2014]
FORMULA
a(n) = Sum_{i=1..n} ( Product_{k|i} A000005(k) ).
EXAMPLE
a(3) = 5. Sum_{i=1..3} ( Product_{k|i} d(k) ) =
( Product_{k|1} d(k) ) + ( Product_{k|2} d(k) ) + ( Product_{k|3} d(k) ) = ( d(1) ) + ( d(1) * d(2) ) + ( d(1) * d(3) ) = 1 + (1)(2) + (1)(2) = 5.
MAPLE
MATHEMATICA
Table[Sum[Product[DivisorSigma[0, k]^(1-Ceiling[i/k]+Floor[i/k]), {k, i}], {i, n}], {n, 50}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, Feb 06 2014
STATUS
approved