n+sigma(n)+sigma(sigma(n)) is a triangular number.

Terms

a(0) =1a(1) =9a(2) =43a(3) =109a(4) =119a(5) =161a(6) =175a(7) =192a(8) =232a(9) =490a(10) =843a(11) =1050a(12) =1162a(13) =1242a(14) =1635a(15) =1959a(16) =2113a(17) =2859a(18) =2935a(19) =3008a(20) =3174a(21) =3469a(22) =3717a(23) =4165a(24) =4173a(25) =4761a(26) =4839a(27) =4876a(28) =5200a(29) =6111