Number of standard Young tableaux with n cells and exactly two successions.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =2a(5) =6a(6) =17a(7) =57a(8) =191a(9) =663a(10) =2415a(11) =9108a(12) =35695a(13) =143989a(14) =599802a(15) =2566917a(16) =11298164a(17) =50967216a(18) =235745644a(19) =1115324000a(20) =5397332497a(21) =26669487517a(22) =134528555379a(23) =691856601631