A333004 a(n) is the smallest squarefree number k such that sum of reciprocals of squarefree numbers up to k (squarefree harmonic sum) exceeds n.

1, 2, 5, 26, 130, 670, 3466, 17985, 93179, 482762, 2501013, 12956855, 67125243, 347753857, 1801596939

Offset

0,2

Comments

The corresponding indices of a(n) in A005117 are 1, 2, 4, 17, 80, 409, 2112, 10936, 56651, 293483, 1520429, ...

Links

Table of n, a(n) for n=0..14.

Eric Weisstein's World of Mathematics, Squarefree

Example

a(2) = 5 because 1/1 + 1/2 + 1/3 = 1.8333... < 2 but 1/1 + 1/2 + 1/3 + 1/5 = 2.0333... > 2.

Crossrefs

Similar sequences: A002387 (for positive integers), A016088 (for primes), A076751 (for composite numbers), A332991 (for prime powers).

Cf. A005117 (squarefree numbers).

Sequence in context: A045903 A090878 A214951 * A120762 A226170 A371614

Adjacent sequences: A333001 A333002 A333003 * A333005 A333006 A333007

Keyword

nonn,hard,more

Author

Ilya Gutkovskiy, Mar 05 2020

Extensions

a(11)-a(14) from Daniel Suteu, Mar 05 2020

Status

approved