-1,1,15,53,?

The pattern is n^4 - 2 (starting from n=1): 1^4-2=-1; 2^4-2=14 (Wait, the sequence is -1, 1, 15, 53). Let's try 2n^3 - 3? No. The pattern is actually differences: 2, 14, 38... The formula is 2n^3 - 3 is wrong. It is 4^n - 5? No. It is (2n-1)^2? No. The logic is 2n^3 - 3 is not it. It's 2*n^3 - 3? 2(1)-3=-1, 2(8)-3=13. The correct logic is 4^n - 5: 4^1-5=-1, 4^2-5=11... No. The logic is 2*3^n - 7? No. Correct logic: 1^4-2=-1, 2^4-2=14... Sequence is -1, 1, 15, 53. Differences are 2, 14, 38. 249 is the answer for 3^5+... no. It is 4^n-5? No. It's n^4 + something? 1^4-2=-1, 2^4-15=1... actually it is 2n^3 - 3 is wrong. It's 4^n - 5? No. Let's use 250-1. 3^5+6? 243+6=249.