We mainly introduce two new kinds of numbers given by
Rn=k=0∑n(kn)(kn+k)2k−11 (n=0,1,2,...) and
Sn=k=0∑n(kn)2(k2k)(2k+1) (n=0,1,2,...). We find
that such numbers have many interesting arithmetic properties. For example, if
p≡1(mod4) is a prime with p=x2+y2 (where x≡1(mod4) and
y≡0(mod2)), then R(p−1)/2≡p−(−1)(p−1)/42x(modp2).
Also, n21k=0∑n−1Sk∈Z and n1k=0∑n−1Sk(x)∈Z[x]for all n=1,2,3,...,
where Sk(x)=∑j=0k(jk)2(j2j)(2j+1)xj. For any positive
integers a and n, we show that, somewhat surprisingly,
n21k=0∑n−1(2k+1)(kn−1)a(k−n−1)a∈Z and n1k=0∑n−14k2−1(kn−1)a(k−n−1)a∈Z.
We also solve a conjecture of V.J.W. Guo and J. Zeng, and pose several
conjectures for further research.