A colourful grid of the first 25 prime numbers. (Chris/flickr), CC BY To define the nth number in the A072666, we take the nth prime number (where “n” stands for a number), add it to the (n+1 ...

The longest series of this kind known at present consists of forty prime numbers. It begins with 41, 43, 47, 53 … and ends with … 1373, 1447,1523,1601, a truly extraordinary sequence.