How to include NaN elements in an array based on a condition?

Can someone help me out in writing a code to insert NaN eleemnts in an array if the element is not a consecutive multiple of 2? For example if a = [2 4 6 12 14 18]; Im expecting to be turned out as a = [2 4 6 NaN NaN 12 14 NaN 18]; Thank you

Answer 1

[Davide Masiello]

a = [2 4 6 12 14 18];
A = a(1):2:a(end);
new_a = zeros(size(A));
idx = any(a'== A,1);
new_a(idx) = a;
new_a(~idx) = nan;
new_a

new_a = 1×9

2 4 6 NaN NaN 12 14 NaN 18