Least n-gonal number greater than 1 such that sigma(n) is also n-gonal.

Terms

a(0) =36a(1) =81a(2) =590a(3) =5286126a(4) =15880a(5) =1932821a(6) =37990539325a(7) =6280a(8) =234222782808a(9) =3350529a(10) =931738a(11) =455621651099a(12) =3312a(13) =2680a(14) =373569353a(15) =1128231876a(16) =47531850550a(17) =601657a(18) =4609261a(19) =115668a(21) =336577944a(22) =40161257476a(23) =5031720a(24) =31424211a(25) =25785a(26) =12670237746