Problem 672

[jaap]

Is "no nothing" a typo for "do nothing"?

Shouldn't there be a floor function around the $\frac{7^K-1}{11}$ term? I don't think there is a universally accepted meaning for a sum where the upper limit for the index variable is not an integer.

[hk]

Is "no nothing" a typo for "do nothing"?

Yes. Corrected.

Shouldn't there be a floor function around the $\frac{7^K-1}{11}$ term? I don't think there is a universally accepted meaning for a sum where the upper limit for the index variable is not an integer.

Please investigate if $\frac{7^K-1}{11}$ isn't an integer for the values of K used in the problem.

[jaap]

Thanks for fixing that hk.

Shouldn't there be a floor function around the $\frac{7^K-1}{11}$ term? I don't think there is a universally accepted meaning for a sum where the upper limit for the index variable is not an integer.

Please investigate if $\frac{7^K-1}{11}$ isn't an integer for the values of K used in the problem.

Fair enough I suppose. Still, it irks me that a definition of H(K) is given as if it holds for any K. I fully accept that you have to assume K is an integer, since this is in the context of an integer problem, but for me it feels like a step too far that it has the unstated assumption that the definition only makes sense for specific integer values of K and is therefore defined only for those values. I appreciate that this may be a minority opinion, and it's no big deal really.
Anyway, I'll move on to trying to solve the problem.

[macgupta]

I agree with jaap. H is poorly defined.