Spectrum generating algebra of the C_(λ)-extended oscillator and multiphoton coherent states

The $C_{\lambda}$-extended oscillator spectrum generating algebra is shown to be a $C_{\lambda}$-extended $(\lambda-1)$th-degree polynomial deformation of su(1,1). Its coherent states are constructed. Their statistical and squeezing properties are studied in detail. Such states include both some Barut-Girardello and the standard $\lambda$-photon coherent states as special cases.