S_n(x) = log_a^1/2x + log_a^1/3x + log_a^1/6x + log_a^1/11x + log_a^1/18x + log_a^1/27x + ...... up to n-terms, where a > 1. If S₂₄(x) = 1093 and S₁₂(2x) = 265, then value of a is equal to ____________.

Let $${1 \over {16}}$$, a and b be in G.P. and $${1 \over a}$$, $${1 \over b}$$, 6 be in A.P., where a, b > 0. Then 72(a + b) is equal to ___________.

Consider an arithmetic series and a geometric series having four initial terms from the set {11, 8, 21, 16, 26, 32, 4}. If the last terms of these series are the maximum possible four digit numbers, then the number of common terms in these two series is equal to ___________.

The total number of 4-digit numbers whose greatest common divisor with 18 is 3, is _________.