Consider a decimal number of k >= 2 digits m = d_(k)*10^(k-1) + d_(k-1)*10^(k-2) + ... + d_(2)*10 + d_(1). a(n) is the least number m such that the n-th iteration of the transform T(m) -> (d_(k) + d_(k-1) mod 10)*10^(k-1) + (d_(k-1) + d_(k-2) mod 10)*10^(k-2) + ... + (d_(2) + d_(1) mod 10)*10 + (d_(1) + d(k) mod 10) returns m, or -1 if no such number exists.
A243993
Consider a decimal number of k >= 2 digits m = d_(k)*10^(k-1) + d_(k-1)*10^(k-2) + ... + d_(2)*10 + d_(1). a(n) is the least number m such that the n-th iteration of the transform T(m) -> (d_(k) + d_(k-1) mod 10)*10^(k-1) + (d_(k-1) + d_(k-2) mod 10)*10^(k-2) + ... + (d_(2) + d_(1) mod 10)*10 + (d_(1) + d(k) mod 10) returns m, or -1 if no such number exists.
Terms
- a(0) =0a(1) =-1a(2) =2684a(3) =505a(4) =22a(5) =-1a(6) =109a(7) =5000005a(8) =-1a(9) =-1a(10) =-1a(11) =-1a(12) =101a(13) =-1a(14) =-1a(15) =50005a(16) =-1a(17) =-1a(18) =-1a(19) =-1a(20) =20000a(21) =-1a(22) =-1a(23) =-1a(24) =100012a(25) =-1a(26) =-1a(27) =-1a(28) =4999449a(29) =-1
External references
- oeis: A243993