Heptagonal numbers with only odd digits.

Terms

a(0) =1a(1) =7a(2) =55a(3) =1177a(4) =3553a(5) =9517a(6) =11799a(7) =13579a(8) =17935a(9) =31753a(10) =71995a(11) =93799a(12) =97713a(13) =117397a(14) =135373a(15) =371911a(16) =377719a(17) =599515a(18) =733597a(19) =777573a(20) =1131313a(21) =1331155a(22) =1371591a(23) =1555119a(24) =3391315a(25) =3731377a(26) =3979717a(27) =5131573a(28) =7137715a(29) =7333353