Select integer x and triangular number y such that 8y=3x^4-2x^2-1.
Prove that y is divisible by 28 - or find a counter-example.
(In reply to computer exploration shows likely true -- no proof
1. You somehow missed x=1 y=0; a valid triangular number
2. You were very close to proof, not verification- all you needed
was to assume a linear recurrence equation and to show that it assures divisibility by 28.
3.Please read my post and ,if needed, comment on it.