Problems & Puzzles: Puzzles

Puzzle 31.- The Average Prime number, APN(k) = S(Pk)/k

Let’s define the "average prime number" APN(k) as S(Pk)/k, where S(Pk) is the sum of the first k prime numbers.

It happens that this number very few times is an integer. I have calculated the first five times it does:

k P(k) S(pk) S(pk)/k
1 2 2 2
23 83 874 38
53 241 5830 110
853 6599 2615298 3066
11869 126551 712377380 60020

Can you get the following 3 cases ?

(see Puzzle 18 for similar questions about sum of consecutive primes)


Jo Yeong Uk (1/12/98) has found the following first three solutions to APN(k). Jack Brennen (21/05/99) found the fourth solution.

k Pk S(Pk) S(Pk)/k Author(s)
117267 154479 86810649294 740282 Jo Yeong Uk
339615 4864121 794712005370 2340038 Jo Yeong Uk
3600489 60686737 105784534314378 29380602 Jo Yeong Uk
96643287 1966194317 92542301212047102 957565746 Jack Brennen

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Giovanni Resta wrote (Nov. 2004):

I found the following 2 new solutions.

i, pi, Si
2664167025, 63481708607, 82704567079549985700
43435512311, 1161468891953, 24733255676526572596026

No other solutions for pi < 4,011,201,392,413.

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