Palindromic nonagonal (or 9-gonal or enneagonal) numbers.

Terms

a(0) =1a(1) =9a(2) =111a(3) =474a(4) =969a(5) =6666a(6) =18981a(7) =67276a(8) =4411144a(9) =6964696a(10) =15444451a(11) =57966975a(12) =448707844a(13) =460595064a(14) =579696975a(15) =931929139a(16) =994040499a(17) =1227667221a(18) =9698998969a(19) =61556965516a(20) =664248842466a(21) =699030030996