OFFSET
1,1
COMMENTS
a(2*n) is odd and a(2*n-1) is twice a prime where n is a positive integer. - David A. Corneth, Dec 03 2023
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(4) = 21 because a(3) = 10, 21 = 3 * 7 is a semiprime > 10, 10 + 21 = 31 is prime, and no smaller semiprime > 10 works.
MAPLE
R:= 4: s:= 4:
for count from 2 to 100 do
for t from s+1 by 2 do
if isprime(s+t) and numtheory:-bigomega(t) = 2 then
R:= R, t; s:= t; break
fi
od
od:
R;
MATHEMATICA
s = {q = 4}; Do[p = q + 1; While[ PrimeOmega[p] != 2, p = p + 2]; AppendTo[s, q = p], {120}]; s
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov and Robert Israel, Dec 02 2023
STATUS
approved