OFFSET
1,1
COMMENTS
LINKS
Danny Rorabaugh, Table of n, a(n) for n = 1..10000
FORMULA
[A007500]^2, sorted.
EXAMPLE
9 is in the list because 9 = 3*3 is a semiprime and reverse(3) = 3 is prime.
143 is in the list because 143 = 11*13 is a semiprime and both reverse(11) = 11 and reverse(13) = 31 are prime.
PROG
(Sage)
reverse = lambda n: sum([10^i*int(str(n)[i]) for i in range(len(str(n)))])
def is_semirp(n):
F = factor(n)
if sum([f[1] for f in F])==2:
r, p = F[0][0], F[-1][0]
if is_prime(reverse(r)) and is_prime(reverse(p)): return True
[a for a in range(1, 356) if is_semirp(a)] # Danny Rorabaugh, Nov 25 2015
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Danny Rorabaugh, Nov 25 2015
STATUS
approved