OFFSET
1,1
COMMENTS
If you graph n vs a(n), interesting patterns begin to emerge. As you go farther along the n-axis, greater are the number of Safe Primes, on average, within each interval obtained. The smallest count of 1 occurs 4 times (terms: 3rd, 5th, 13th, and 17th) in the sequence above. I suspect the number of Safe Primes within each interval will never be zero. If one could prove this, then it would imply that Safe Primes are infinite. Can you prove it?
LINKS
Jaspal Singh Cheema, Table of n, a(n) for n = 1..10177
Rick Aster, Prime number sieve, SAS prime sieve program
Wikipedia, Safe prime
EXAMPLE
Take any pair of consecutive primes. Let us say the very first one (2,3). Square both terms to obtain an interval (4,9). Within this interval, there are two Safe Primes, namely 5 and 7. Hence the very first term of the sequence above is 2. Similarly, the next term, 2, refers to the two Safe Primes between squares of (3,5), or the interval (9,25), which are 11 and 23.
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaspal Singh Cheema, Mar 10 2010
EXTENSIONS
Edited by D. S. McNeil, Nov 17 2010
STATUS
approved