A083815 Semiprimes whose prime factors are distinct and the reversal of one factor is equal to the other.

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

Robert Israel, Table of n, a(n) for n = 1..10000

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

Cf. A001358, A006567, A109308.

Sequence in context: A097740 A325151 A213605 * A250893 A261857 A379125

Adjacent sequences: A083812 A083813 A083814 * A083816 A083817 A083818

Keyword

base,nonn

Author

Jason Earls, Jun 17 2003

Extensions

More terms from Ray Chandler, Jul 22 2003

Status

approved