A248981 Sequence of distinct least positive numbers such that the average of the first n terms is prime.

2, 4, 3, 11, 5, 17, 7, 39, 29, 13, 57, 41, 19, 75, 23, 119, 63, 31, 145, 37, 121, 85, 43, 139, 47, 203, 53, 221, 59, 299, 67, 195, 71, 343, 79, 223, 83, 311, 89, 409, 97, 265, 101, 189, 103, 287, 107, 395, 113, 813, 127, 335, 131, 455, 137, 249, 709, 149, 267, 151, 517, 157, 535, 163, 423, 167, 569, 173, 587, 179, 321, 181, 911, 191

Offset

1,1

Comments

1 will not appear in this sequence. Which numbers will not appear? Is it a finite set of numbers?

Links

Table of n, a(n) for n=1..74.

Example

1/1 = 1 is not prime. 2/1 = 2 is prime. So a(1) = 2.
(2+1)/2 is not prime. (2+3)/2 is not prime. (2+4)/2 = 3 is prime. So a(2) = 4.
(2+4+1)/3 is not prime. (2+4+3)/3 = 3 is prime. So a(3) = 3.
This process continues.

Prog

(PARI) v=[2]; n=1; while(#v<200, s=(n+vecsum(v))/(#v+1); if(type(s)=="t_INT", if(isprime(s)&&!vecsearch(vecsort(v), n), v=concat(v, n); n=0)); n++); v

Crossrefs

Cf. A000040, A073883.

Sequence in context: A305423 A271866 A093839 * A096780 A376904 A332454

Adjacent sequences: A248978 A248979 A248980 * A248982 A248983 A248984

Keyword

nonn

Author

Derek Orr, Oct 18 2014

Status

approved