OFFSET
1,1
COMMENTS
Semiprime analog of A007522 Primes of form 8n+7. These semiprimes must all be numbers of the form 4^i(8j+7), i >= 0, j >= 0. However, for positive i, 4^i(8j+7) has more than 2 prime factors (with multiplicity). Hence from Legendre's corollary to Lagrange's Four-Square Theorem, this sequence is precisely Semiprimes of the form 8*k+7.
MATHEMATICA
Select[8*Range[200]+7, PrimeOmega[#]==2&] (* Harvey P. Dale, Oct 28 2017 *)
CROSSREFS
KEYWORD
easy,nonn,less
AUTHOR
Jonathan Vos Post, Aug 08 2006
EXTENSIONS
a(15)-a(52) from Giovanni Resta, Jun 13 2016
STATUS
approved