Problems & Puzzles: Puzzles Puzzle 193. The Andersen's theorem & primes Very recently, 9 April 2002, Joseph L. Pe (1, 2, 3) defined the "pictureperfect numbers (ppn)" the following way:
Here are the known earliest seven ppn numbers, as consigned in the EIS, A069942: 6, 10311, 21661371, 1460501511, 7980062073, 79862699373, 798006269373 The ppn definition seems so fancy that one would hardly expect to find an interesting theorem associated to the ppn numbers. Nevertheless, this is exactly what was achieved by Jens Kruse Andersen:
Honoring the author of this theorem, any prime of this type p=140{(0)_{z}10(9)_{n}89}_{k} is named Andersen's prime. See the earliest Andersen primes at A075130 and the corresponding ppn numbers at A075131 Using this form Andersen has told me by email that he has produced many large primes  and the ppns associated  being the largest prime a 2461 digits one, 140*10^2458+1089, verified by PRIMO). Moreover, Andersen has some empirical evidence that suggests that there are infinite Andersen's primes On the other hand, a fast examination of the known earliest seven ppn numbers shows that the first four ppn numbers are out of the Andersen's rule. This may be indicative that it could exists some other theorems similar, to the Andersen's one, waiting to be discovered. In any case, all known ppn numbers (other than 6) are odd and divided by 3. As a matter of fact Mark Ganson conjectures that every ppn is divided by 3. The logical questions are:
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