Number of parallelogram polyominoes with n cells (also called staircase polyominoes, although that term is overused).

A006958

Number of parallelogram polyominoes with n cells (also called staircase polyominoes, although that term is overused).

Terms

    a(0) =1a(1) =2a(2) =4a(3) =9a(4) =20a(5) =46a(6) =105a(7) =242a(8) =557a(9) =1285a(10) =2964a(11) =6842a(12) =15793a(13) =36463a(14) =84187a(15) =194388a(16) =448847a(17) =1036426a(18) =2393208a(19) =5526198a(20) =12760671a(21) =29466050a(22) =68041019a(23) =157115917a(24) =362802072a(25) =837759792a(26) =1934502740a(27) =4467033943a(28) =10314998977a(29) =23818760154

External references