Find formula Number Sequences of

Question

3, 10, 31, 94,.....

Answer 1

not arithmetic nor geometric
gave up and checked with Wolfram

found:
term(n) = (7(3^n) - 3)/6

http://www.wolframalpha.com/input/?i=pattern+%7B3,+10,+31,+94%7D

quite obscure, perhaps more terms would have helped.