OFFSET
1,1
LINKS
Jianing Song, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = (A348421(n) + 3)/2.
EXAMPLE
25 is a term since 25 is an odd composite number and 2*25 - 3 = 47 is prime.
MATHEMATICA
Select[Range[1, 700, 2], CompositeQ[#] && PrimeQ[2*# - 3] &] (* Amiram Eldar, Oct 18 2021 *)
PROG
(PARI) isA348423(n) = !isprime(n) && (n%2) && isprime(2*n-3)
CROSSREFS
KEYWORD
nonn,easy,changed
AUTHOR
Jianing Song, Oct 18 2021
STATUS
approved