Published online by Cambridge University Press: 20 November 2018
In 1970, Kotzig and Rosa defined the concept of edge-magic labelings as follows. Let   $G$  be a simple
 $G$  be a simple   $\left( p,\,q \right)$ -graph (that is, a graph of order
 $\left( p,\,q \right)$ -graph (that is, a graph of order   $p$  and size
 $p$  and size   $q$  without loops or multiple edges). A bijective function
 $q$  without loops or multiple edges). A bijective function   $f:\,V\left( G \right)\cup E\left( G \right)\,\to \,\left\{ 1,\,2,\,.\,.\,.\,,\,p\,+\,q \right\}$  is an edge-magic labeling of
 $f:\,V\left( G \right)\cup E\left( G \right)\,\to \,\left\{ 1,\,2,\,.\,.\,.\,,\,p\,+\,q \right\}$  is an edge-magic labeling of   $G$  if
 $G$  if   $f\left( u \right)\,+\,f\left( uv \right)\,+f\left( v \right)\,=\,k$ , for all
 $f\left( u \right)\,+\,f\left( uv \right)\,+f\left( v \right)\,=\,k$ , for all   $uv\,\in \,E\left( G \right)$ . A graph that admits an edge-magic labeling is called an edge-magic graph, and
 $uv\,\in \,E\left( G \right)$ . A graph that admits an edge-magic labeling is called an edge-magic graph, and   $k$  is called the magic sum of the labeling. An old conjecture of Godbold and Slater states that all possible theoretical magic sums are attained for each cycle of order
 $k$  is called the magic sum of the labeling. An old conjecture of Godbold and Slater states that all possible theoretical magic sums are attained for each cycle of order   $n\,\ge \,7$ . Motivated by this conjecture, we prove that for all
 $n\,\ge \,7$ . Motivated by this conjecture, we prove that for all   ${{n}_{0}}\,\in \,\mathbb{N}$ , there exists
 ${{n}_{0}}\,\in \,\mathbb{N}$ , there exists   $n\,\in \,\mathbb{N}$  such that the cycle
 $n\,\in \,\mathbb{N}$  such that the cycle   ${{C}_{n}}$  admits at least
 ${{C}_{n}}$  admits at least   ${{n}_{0}}$  edge-magic labelings with at least
 ${{n}_{0}}$  edge-magic labelings with at least   ${{n}_{0}}$  mutually distinct magic sums. We do this by providing a lower bound for the number of magic sums of the cycle
 ${{n}_{0}}$  mutually distinct magic sums. We do this by providing a lower bound for the number of magic sums of the cycle   ${{C}_{n}}$ , depending on the sum of the exponents of the odd primes appearing in the prime factorization of
 ${{C}_{n}}$ , depending on the sum of the exponents of the odd primes appearing in the prime factorization of   $n$ .
 $n$ .
The first and the third author are supported by the Spanish Research Council under project MTM2011-28800-C02-01 and by the Catalan Research Council under grant 2009SGR1387.
 and other related topics. Ars Combin., to appear.Google Scholar
 and other related topics. Ars Combin., to appear.Google Scholar