Two new expansions for partial sums of Gauss' triangular and square numbers
series are given. As a consequence, we derive a family of inequalities for the
overpartition function $\bar{p}(n)$ and for the partition function $p_1(n)$
counting the partitions of $n$ with distinct odd parts. Some further
inequalities for variations of partition function are proposed as conjectures.
Motivated by the recent work of Chu [Electron. J. Combin. 17 (2010), #N24],
we give simple proofs of Jensen's identity $$ \sum_{k=0}^{n}{x+kz\choose
k}{y-kz\choose n-k} =\sum_{k=0}^{n}{x+y-k\choose n-k}z^k, $$ and Chu's and
Mohanty-Handa's generalizations of Jensen's identity. We also give a quite
simple proof of an equivalent form of Graham-Knuth-Patashnik's identity $$
\sum_{k\geq 0}{m+r\choose m-n-k}{n+k\choose n}x^{m-n-k}y^k =\sum_{k\geq
0}{-r\choose m-n-k}{n+k\choose n}(-x)^{m-n-k}(x+y)^k, $$ which was
rediscovered, respectively, by Sun in 2003 and Munarini in 2005.
By using the Newton interpolation formula, we generalize the recent
identities on the Catalan triangle obtained by Miana and Romero as well as
those of Chen and Chu. We further study divisibility properties of sums of
products of binomial coefficients and an odd power of a natural number. For
example, we prove that for all positive integers $n_1, ..., n_m$,
$n_{m+1}=n_1$, and any nonnegative integer $r$, the expression
$$n_1^{-1}{n_1+n_{m}\choose n_1}^{-1} \sum_{k=1}^{n_1}k^{2r+1}\prod_{i=1}^{m}
{n_i+n_{i+1}\choose n_i+k}$$ is either an integer or a half-integer.