a(n) = n-th positive integer k such that tan(k-1) <= 0 and tan(k) > 0.

Terms

a(0) =1a(1) =4a(2) =7a(3) =10a(4) =13a(5) =16a(6) =19a(7) =22a(8) =26a(9) =29a(10) =32a(11) =35a(12) =38a(13) =41a(14) =44a(15) =48a(16) =51a(17) =54a(18) =57a(19) =60a(20) =63a(21) =66a(22) =70a(23) =73a(24) =76a(25) =79a(26) =82a(27) =85a(28) =88a(29) =92