A number of 50 digits has all its digits equal to 1 except the 26th digit. If the number is divisible by 13, then find the digit in the 26th place.

(In reply to re(3): solution by Richard)

(10^n)%11=(-1)^n should have been (10^n)%11=((-1)^n)%m since by remainder I mean least nonnegative remainder as is usual in long division. Notice that this does NOT give negatives (quotient or remainder) for the negative of a positive integer: 12=5*2+2 but -12=5*(-3)+3 so that 12%5=2 but (-12)%5=3.

Posted by Richard on 2003-11-22 12:54:55