Composite numbers n such that juxtaposition of prime factors of n has length 4.

Terms

a(0) =16a(1) =24a(2) =36a(3) =40a(4) =44a(5) =52a(6) =54a(7) =56a(8) =60a(9) =66a(10) =68a(11) =76a(12) =78a(13) =81a(14) =84a(15) =90a(16) =92a(17) =99a(18) =100a(19) =102a(20) =110a(21) =114a(22) =116a(23) =117a(24) =121a(25) =124a(26) =126a(27) =130a(28) =135a(29) =138