Each entry is the product of p and p+2 where both p and p+2 are prime, i.e., the product of the lesser and greater of a twin prime pair.

Except for the first term, all entries have digital root 8. - Lekraj Beedassy, Jun 11 2004

The above statement follows from p>3 => (p,p+2)=(6k-1,6k+1) => p(p+2)=36k^2-1=8 (mod 9), and A010888=A010878 (mod 9). - M. F. Hasler, Jan 11 2013

Albert A. Mullin states that m is a product of twin primes iff phi(m)*sigma(m) = (m-3)*(m+1), where phi(m) = A000010(m) and sigma(m) = A000203(m). Of course, for a product of distinct primes p*q we know sigma(p*q) = (p+1)*(q+1) and if p, q, are twin primes, say q = p + 2, then sigma(p*q) = (p+1)*(q+1) = (p+1)*(p+3). - Jonathan Vos Post, Feb 21 2006

Also the area of twin prime rectangles. A twin prime rectangle is a rectangle whose sides are components of twin prime pairs. E.g., The twin prime pair (3,5) produces a 3 X 5 unit rectangle which has area 15 square units. - Cino Hilliard, Jul 28 2006

Except for 15, a product of twin primes is of the form 36k^2-1 (cf. A136017, A002822). - Artur Jasinski, Dec 12 2007

A072965(a(n)) = 1; A072965(m) mod A037074(n) > 0 for all m. - Reinhard Zumkeller, Jan 29 2008

The number of terms less than 10^(2n) is A007508(n). - Robert G. Wilson v, Feb 08 2012

Solutions of the equation n'=2*sqrt(n+1), where n' is the arithmetic derivative of n. - Paolo P. Lava, Oct 30 2012

If m is the product of twin primes, then sigma(m) = m + 1 + 2*sqrt(m + 1), phi(m) = m + 1 - 2*sqrt(m + 1). pmin(m) = sqrt(m + 1) - 1, pmax(m) = sqrt(m + 1) + 1. - Wesley Ivan Hurt, Jan 06 2013

Subset of A210503. - Paolo P. Lava, Jan 28 2013