where w and aj have positive real part and s has real part greater than N.
It has a meromorphic continuation to all complex s, whose only singularities are simple poles at s = 1, 2, ..., N. For N = w = a1 = 1 it is the Riemann zeta function.
Barnes, E. W. (1901), "The Theory of the Double Gamma Function", Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character, 196 (274–286), The Royal Society: 265–387, Bibcode:1901RSPTA.196..265B, doi:10.1098/rsta.1901.0006, ISSN0264-3952, JSTOR90809
Barnes, E. W. (1904), "On the theory of the multiple gamma function", Trans. Camb. Philos. Soc., 19: 374–425