a(n+1) = a(n) written in base 7 (read in base 10); a(1) = 7.

Terms

a(0) =7a(1) =10a(2) =13a(3) =16a(4) =22a(5) =31a(6) =43a(7) =61a(8) =115a(9) =223a(10) =436a(11) =1162a(12) =3250a(13) =12322a(14) =50632a(15) =300421a(16) =2360602a(17) =26031136a(18) =434155345a(19) =13521155011a(20) =656031631000