A new mathematical concept, the nested summation symbol (NSS) has been
developed. This concept is attached to a mathematical linear operator
directly related to the summation symbols. After a discussion on its
properties, we investigate the potential usefulness of this symbol in
the developing of sequential and parallel computational algorithms, co
nstituting a powerful link between mathematical formalism and high lev
el languages programming. A NSS is well suited in order to express som
e kind of mathematical formulae and to implement them in any computati
onal environment. In this sense, NSSs are directly related to artifici
al intelligence techniques. Nested sums are connected with generalized
nested do loop (GNDL) structures, a programming concept developed in
our laboratory. This paper shows an application of the NSS. The NSS co
ncept has been used to obtain in a compact form the expressions of the
general energy and wavefunction corrections associated to the perturb
ation theory under the Brillouin-Wigner or the Rayleigh-Schrodinger fo
rmalisms.