Position of n-th 7 in A031087.

Terms

a(0) =7a(1) =23a(2) =41a(3) =59a(4) =77a(5) =95a(6) =113a(7) =118a(8) =120a(9) =122a(10) =124a(11) =126a(12) =128a(13) =130a(14) =131a(15) =132a(16) =134a(17) =149a(18) =174a(19) =201a(20) =228a(21) =255a(22) =282a(23) =309a(24) =336a(25) =343a(26) =346a(27) =349a(28) =352a(29) =355