OFFSET
0,2
LINKS
Chai Wah Wu, Table of n, a(n) for n = 0..10000
N. J. A. Sloane, Families of Essentially Identical Sequences, Mar 24 2021 (Includes this sequence)
FORMULA
a(n) = (2*n+1)^2 + Sum_{i=2..2n+1} (2*n+2-i)*(4*n+4-i)*phi(i). - Chai Wah Wu, Aug 17 2021
PROG
(Python)
from sympy import totient
def A331759(n): return (2*n+1)**2 + sum(totient(i)*(2*n+2-i)*(4*n+4-i) for i in range(2, 2*n+2)) # Chai Wah Wu, Aug 17 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Feb 04 2020
STATUS
approved