Mountain emirps.

Terms

a(0) =1231a(1) =1321a(2) =1381a(3) =1471a(4) =1741a(5) =1831a(6) =12491a(7) =12641a(8) =12841a(9) =13591a(10) =13751a(11) =13781a(12) =13841a(13) =14591a(14) =14621a(15) =14821a(16) =14831a(17) =14891a(18) =15731a(19) =15791a(20) =18731a(21) =19421a(22) =19531a(23) =19541a(24) =19751a(25) =19841a(26) =123731a(27) =123821a(28) =124951a(29) =124981