1,1

The primes are = (sum of numbers from 1 to n)/2 + or - 1

Table of n, a(n) for n=1..41.

3*4/4=3 3-1=2 prime so a(1)=3

7*8/4=14 14-1=13 prime so a(2)=7

8*9/4=18 18-1=17 prime 18+1=19 prime so a(3)=8

Sequence in context: A002381 A131559 A051211 * A309197 A076683 A045542

Adjacent sequences: A105170 A105171 A105172 * A105174 A105175 A105176

nonn

Pierre CAMI, Apr 11 2005

approved