OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(3) = 110 is a member because 110 = 37+73 where 37 is an emirp.
MAPLE
revdigs:= proc(n) local L, i; L:= convert(n, base, 10); add(L[-i]*10^(i-1), i=1..nops(L)) end proc:
f:= proc(n) local r;
if not isprime(n) then return NULL fi;
r:= revdigs(n);
if r > n and isprime(r) then return r+n fi
end proc:
S:= map(f, {seq(seq(seq(i*10^d+j, j=1..10^d-1, 2), i=[1, 3, 7, 9]), d=1..4)}):
sort(convert(S, list));
PROG
(Python)
from sympy import isprime, nextprime
def epgen(start=1, end=float('inf')): # generates unique emirp/prime pairs
p = nextprime(start-1)
while p <= end:
revp = int(str(p)[::-1])
if p < revp and isprime(revp): yield (p, revp)
p = nextprime(p)
def aupto(lim):
epsums = set(sum(ep) for ep in epgen(1, lim))
return sorted(filter(lambda x: x<=lim, epsums))
print(aupto(11111)) # Michael S. Branicky, Jun 18 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Jun 18 2021
STATUS
approved