The preposition dan is more frequent than an.
Source: Neumann 1985: 309
Source: Klingler 2003: 360
Source: Valdman et al. 1998: 107
Source: Valdman et al. 1998: 41
Source: Neumann 1985: 368
Source: Neumann 1985: 382
Source: Neumann 1985: 299
Source: Neumann 1985: 301