%I #15 Jun 25 2017 13:18:28

%S 0,1,2,3,4,5,7,9,11,13,15,17,19,21,23,25,28,31,34,37,40,43,46,49,52,

%T 55,58,61,64,67,70,73,77,81,85,89,93,97,101,105,109,113,117,121,125,

%U 129,133,137,141,145,149,153,157,161,165,169,174,179,184,189,194,199

%N Sum of the integer part of 5/2-th roots of integers less than or equal to n.

%F a(0) = 0, a(n) = a(n - 1) + floor(n^(2/5)). - _Alonso del Arte_, Jun 18 2017

%F a(n) = (5/7)*n^(7/5) + O(n). - _Charles R Greathouse IV_, Jun 25 2017

%e 1^(2/5) = 1.

%e 2^(2/5) = 1.3195...

%e 3^(2/5) = 1.5518...

%e 4^(2/5) = 1.7411...

%e 5^(2/5) = 1.90365...

%e 6^(2/5) = 2.047672511...

%e Hence a(1) = 1, a(2) = 2, a(3) = 3, a(4) = 4, a(5) = 5, a(6) = 7.

%t Accumulate[Table[Floor[n^(2/5)], {n, 0, 59}]] (* _Alonso del Arte_, Jun 13 2017 *)

%o (PARI) a(n)=sum(k=1,n, sqrtnint(k^2,5)) \\ _Charles R Greathouse IV_, Jun 25 2017

%K nonn,easy

%O 0,3

%A Michel Tixier (tixier(AT)dyadel.net)