Why doesn't basepoint G of Secp256K1 seem to be on the Elliptic Curve?
The secp256k1 curve is defined over x and y coordinates that are members of the finite field GF(2^256 - 2^32 - 977), or in other words, their operations hold only when considered modulo 115792089237316195423570985008687907853269984665640564039457584007908834671663.

55066263022277343669578718895168534326250603453777594175500187360389116729240^3 - (32670510020758816978083085130507043184471273380659243275938904335757337482424^2 + 7) is exactly 1442042049659660869506300006036683750029629333882594701370927246876626245108435922902327776681700708714008192087431130951749952236093997894375239788520937 times 115792089237316195423570985008687907853269984665640564039457584007908834671663.