A342365 The primes associated with A239800 (1 if A239800(n) = 0).
3, 17, 73, 337, 191, 709, 1289, 3137, 3313, 3181, 7349, 5449, 8243, 11621, 7681, 16673, 17477, 28657, 27893, 74441, 71023, 87869, 94439, 33889, 250301, 298013, 205957, 131489, 327179, 87961, 1178993, 354689, 1769791, 595817, 1304591, 417169, 2343359
Offset: 1
Keywords
Examples
The smallest m such that 2*m*i + 1 is not prime until i = 3 is m = 12, and the corresponding prime is 2*12*3 + 1 = 73 = a(3). The smallest m such that 2*m*i + 1 is not prime until i = 4 is m = 42, and the corresponding prime is 2*42*4 + 1 = 337 = a(4). The smallest m such that 2*m*i + 1 is not prime until i = 5 is m = 19, and the corresponding prime is 2*19*5 + 1 = 191 = a(5).
Links
- Jianing Song, Table of n, a(n) for n = 1..100
Programs
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PARI
isok(n, m) = for(i=1, n-1, if(isprime(2*m*i+1), return(0))); if(isprime(2*m*n+1), 1, 0) a(n) = for(m=1, oo, if(isok(n, m), return(2*n*m+1))) \\ based on the conjecture that all numbers occur in A016014
Formula
a(n) = 2*n*A239800(n)+1.