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A345409 Numbers that are the sum of an emirp and its reversal. 3
44, 88, 110, 176, 424, 808, 908, 928, 1070, 1090, 1150, 1190, 1312, 1372, 1616, 1676, 1736, 2222, 2332, 2552, 2662, 2992, 3212, 4114, 4334, 4444, 4664, 4774, 4994, 5104, 5324, 5434, 6226, 6776, 6886, 7106, 7436, 8338, 8558, 8998, 9218, 9328, 9548, 10010, 10120, 10450, 10670, 10780, 11000, 11110 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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
Sequence in context: A195816 A118087 A335481 * A246412 A248365 A044182
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Jun 18 2021
STATUS
approved

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Last modified July 17 05:50 EDT 2024. Contains 374360 sequences. (Running on oeis4.)