a(1) = 1; for n>1, a(n) = the largest prime divisor of the number C(n) formed from the concatenation of n, n-1, n-2, n-3, ... down to 1.

A075021

a(1) = 1; for n>1, a(n) = the largest prime divisor of the number C(n) formed from the concatenation of n, n-1, n-2, n-3, ... down to 1.

Terms

    a(0) =1a(1) =7a(2) =107a(3) =149a(4) =953a(5) =218107a(6) =402859a(7) =4877a(8) =379721a(9) =54421a(10) =370329218107a(12) =237927839a(13) =1728836281a(16) =677181889a(17) =399048049

External references