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

Author

Jason Earls, Jun 17 2003

Keywords

• base
• nonn

Comments

Products of emirp pairs, sorted. - Lekraj Beedassy, Jan 10 2008

Examples

			a(2)= 1207 = 17 * 71.
		

Links

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

Crossrefs

Cf. A001358, A006567, A109308.

Programs

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

Extensions

More terms from Ray Chandler, Jul 22 2003