Triangular numbers k such that phi(k) is also a triangular number, where phi(k) is the Euler totient function (A000010).

A287472

Triangular numbers k such that phi(k) is also a triangular number, where phi(k) is the Euler totient function (A000010).

Terms

    a(0) =1a(1) =231a(2) =1035a(3) =6786a(4) =190036a(5) =193131a(6) =766941a(7) =1237951a(8) =1348903a(9) =3069003a(10) =3396921a(11) =8034036a(12) =9152781a(13) =11875501a(14) =15694003a(15) =28001386a(16) =29587278a(17) =35149920a(18) =61643856a(19) =63196903a(20) =130758706a(21) =178161126a(22) =198214005a(23) =227751153a(24) =268111746a(25) =339210081a(26) =402102261a(27) =654224878

External references