A360297 - OEIS

A360297

a(n) = minimal positive k such that the sum of the primes prime(n) + prime(n+1) + ... + prime(n+k) is divisible by prime(n+k+1), or -1 if no such k exists.

1, 3, 7, 11, 26, 20, 27, 52, 1650, 142, 53, 168234, 212, 7, 13

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OFFSET

1,2

COMMENTS

In the first 100 terms there are twenty values for which a(n) is currently unknown; for all of these values a(n) is at least 10^9. These unknown terms are for n = 16, 22, 24, 34, 41, 42, 45, 48, 50, 54, 55, 62, 68, 70, 72, 75, 80, 87, 88, 98. In this same range the largest known value is a(76) = 749597506, where prime(76) = 383 leads to a sum of primes of 6173644601523754801 that is divisible by 16865554301.

See A360311 for the sum of the k+1 primes. See A360312 for prime(n+k+1).

LINKS

Table of n, a(n) for n=1..15.

Scott R. Shannon, Terms for n = 1..100. The terms currently unknown are set to -1.

EXAMPLE

a(1) = 1 as prime(1) + prime(2) = 2 + 3 = 5, which is divisible by prime(3) = 5.

a(4) = 11 as prime(4) + ... + prime(15) = 7 + 11 + 13 + 17 + 19 + 23 + 29 + 31 + 37 + 41 + 43 + 47 = 318, which is divisible by prime(16) = 53.

PROG

(Python)

from sympy import prime, nextprime

def A360297(n):

p = prime(n)