[seqfan] A008441 Number of ways of writing n as the sum of 2 triangular numbers

[Georgi Guninski]

In the comments:
"Fine gives an explicit formula for a(n) in terms of the divisors of n."

What is this explicit formula?

Since a(n) = A002654(4n+1) it will give some information about the divisors of $4n+1$ assuming just n is factored.