Question

What is the rule for the sequence 3,4,7,12?

Answer 1

Looks like you add increasing odd numbers, +1, +3, +5, +7, etc to the previous in sequence to get the next.

Explanation:

Look for a pattern or reason for the next number in the sequence.
In this case 3+1=4, 4+3=7, 7+5=12, so probable answer is to add the next odd number to the last one in the sequence to get the next.