@ARTICLE{
author={de la Pena Jose Antonio,Gutman Ivan,Rada Juan},
year={2008},
title={Retarded regular graphs are regular or semiregular},
journal={LINEAR & MULTILINEAR ALGEBRA},
volume={56},
number={5},
pages={507-509},
document_type={Article},
} 

@ARTICLE{
author={de la Pena Jose Antonio,Gutman Ivan,Rada Juan},
year={2007},
title={Estimating the Estrada index},
journal={LINEAR ALGEBRA AND ITS APPLICATIONS},
volume={427},
number={1},
pages={70-76},
document_type={Article},
} 

@ARTICLE{
author={Gutman Ivan,Firoozabadi Sanaz Zare,de la Pena Jose Antonio,Rada Juan},
year={2007},
title={On the energy of regular graphs},
journal={MATCH-COMMUNICATIONS IN MATHEMATICAL AND IN COMPUT},
volume={57},
number={2},
pages={435-442},
document_type={Article},
} 

@ARTICLE{
author={Zhou Bo,Gutman Ivan,de la Pena Jose Antonio,Rada Juan,Mendoza L},
year={2007},
title={On spectral moments and energy of graphs},
journal={MATCH-COMMUNICATIONS IN MATHEMATICAL AND IN COMPUT},
volume={57},
number={1},
pages={183-191},
document_type={Article},
}