Palindromic heptagonal numbers.

Terms

a(0) =0a(1) =1a(2) =7a(3) =55a(4) =616a(5) =3553a(6) =4774a(7) =60606a(8) =848848a(9) =4615164a(10) =5400045a(11) =6050506a(12) =7165445617a(13) =62786368726a(14) =65331413356a(15) =73665056637a(16) =91120102119a(17) =345546645543a(18) =365139931563a(19) =947927729749