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A083815
Semiprimes whose prime factors are distinct and the reversal of one factor is equal to the other.
8
403, 1207, 2701, 7663, 35143, 75007, 117907, 127087, 140209, 173809, 197209, 247021, 257821, 342127, 382387, 643063, 692443, 743623, 1226221, 1341331, 1626151, 1698661, 1739161, 2073991, 2138791, 2528611, 2561011, 3321133
OFFSET
1,1
COMMENTS
Products of emirp pairs, sorted. - Lekraj Beedassy, Jan 10 2008
LINKS
EXAMPLE
a(2)= 1207 = 17 * 71.
MAPLE
revdigs:= proc(n) local i, L;
L:= convert(n, base, 10);
add(L[-i]*10^(i-1), i=1..nops(L))
end proc:
f:= proc(p) local r;
if not isprime(p) then return NULL fi;
r:= revdigs(p);
if r > p and isprime(r) then r*p fi
end proc:
sort(map(f, [seq(i, i=13..9999, 2)])); # Robert Israel, Dec 26 2018
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Jason Earls, Jun 17 2003
EXTENSIONS
More terms from Ray Chandler, Jul 22 2003
STATUS
approved