15, 29, 56, 108, 208⦠- Tetranacci numbers: a(n) = a(n-1) + a(n-2) + a(n-3) +a(n-4)
13, -21, 34, -55, 89⦠- Signed Fibonacci numbers: a(n+2)=-a(n+1)+a(n)
52, 56, 48, 64, 32..... - Looks like some kind of spherical coordinate system (cant help you here)