A331760 a(n) = A115004(2n)/4.

2, 20, 83, 237, 534, 1054, 1892, 3114, 4880, 7327, 10530, 14730, 20066, 26689, 34882, 44902, 56850, 70946, 87644, 106986, 129470, 155457, 184920, 218596, 256675, 299292, 347261, 400590, 459615, 525217, 597887, 677507, 764657, 860340, 964291, 1077693, 1201321

Offset: 1

Author

N. J. A. Sloane, Feb 04 2020

Keywords

• nonn

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..10000
• N. J. A. Sloane, Families of Essentially Identical Sequences, Mar 24 2021 (Includes this sequence)

Crossrefs

Cf. A115004, A331759.

Programs

Python

from sympy import totient
def A331760(n): return n**2 + sum(totient(i)*(2*n+1-i)*(4*n+2-i) for i in range(2,2*n+1))//4 # Chai Wah Wu, Aug 17 2021

Formula

a(n) = n^2 + (Sum_{i=2..2n} (2*n+1-i)*(4*n+2-i)*phi(i))/4. - Chai Wah Wu, Aug 17 2021