I'm looking for papers or recent results on the hypertriangular function of $n$:
$$H_t(n)= \displaystyle\sum\limits_{k=1}^{n} k^k$$
This is A001923 in the OEIS.
I don't have much experience with sums like this, but what makes finding a closed form so much more difficult that similar-looking sums such as the ones that appear in the "Sophomore's dream" identities?