Position of n-th 4 in A031269.

Terms

a(0) =10a(1) =14a(2) =20a(3) =24a(4) =26a(5) =33a(6) =34a(7) =39a(8) =45a(9) =47a(10) =51a(11) =60a(12) =68a(13) =78a(14) =80a(15) =85a(16) =86a(17) =88a(18) =91a(19) =92a(20) =101a(21) =109a(22) =114a(23) =125a(24) =128a(25) =130a(26) =144a(27) =148a(28) =152a(29) =158