OFFSET
1,1
COMMENTS
Broughan & Qizhi show that this sequence has relative density 2A in the primes, where A = A005596 is Artin's constant. Consequently, there exists a flat number between x and (1+e)x for every e > 0 and large enough x.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Kevin Broughan and Zhou Qizhi, Flat primes and thin primes, Bulletin of the Australian Mathematical Society 82:2 (2010), pp. 282-292.
Qizhi Zhou, Multiply perfect numbers of low abundancy, PhD thesis (2010)
FORMULA
a(n) ~ k * n * log(n) with k = 1/(2A) = 1.3370563...
PROG
(PARI) is(n)=issquarefree((n+1)>>valuation(n+1, 2)) && isprime(n) && n>2 \\ Charles R Greathouse IV, Mar 26 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Charles R Greathouse IV, Jul 11 2011
STATUS
approved