2183005

Appears in sequences

• Triangular numbers of the form k^2 + k - 1.at n=4A217758
• a(n) = A305312(n)/4 if A305312(n)is even and a(n) = (A305312(n) - 1)/4 if A305312(n) is odd, for n >= 1.at n=12A308687