If I want to find the number of '1' digits in an integer, I can design a verb c1, (count ones) to do that:
*c1=.{{+/1=10#.^:_1]y}}"0* Test it: * c1 10* *1* * c1 11* *2* * c1 103416* *2* * c1 56161764121* *4* I can also find the total number of '1' digits in a list of sequential integers from 1 to n: * to=:[+i.@:>:@-~ * * +/c1 1 to n=.30* *13* * +/c1 1 to n=.521* *213* My question is: Given the total number of 1s in a sequence from 1 to n, what is n? A verb F(x) should return the final integer n, in the sequential list 1 to n, that contains x ones. Using the previous results as an example: * F 213 *NB. A sequence 1 to n has 213 ones. What is n? *521 *NB. The sequence 1 to 521 has 213 ones What are some options to design the verb F? 1) Explicit 2) Implicit 3) Iteration 4) Recursion Skip Cave Cave Consulting LLC ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm