a(n) is the least k such that k-n and k are adjacent powerful numbers.

Terms

a(0) =9a(1) =27a(2) =4a(3) =8a(4) =32a(5) =214375a(6) =16a(7) =72a(8) =25a(9) =2197a(10) =3136a(11) =512a(12) =49a(13) =30459375a(14) =64a(15) =144a(16) =529a(17) =243a(18) =100a(19) =21316a(20) =1352a(21) =100489a(22) =648a(23) =1024a(24) =169a(25) =11907a(26) =196a(27) =1000a(28) =36992a(29) =6889