Number of entries in first n rows of Pascal's triangle not divisible by 3.

Terms

a(0) =1a(1) =3a(2) =6a(3) =8a(4) =12a(5) =18a(6) =21a(7) =27a(8) =36a(9) =38a(10) =42a(11) =48a(12) =52a(13) =60a(14) =72a(15) =78a(16) =90a(17) =108a(18) =111a(19) =117a(20) =126a(21) =132a(22) =144a(23) =162a(24) =171a(25) =189a(26) =216a(27) =218a(28) =222a(29) =228