A066737 Composite numbers that are concatenations of primes.

22, 25, 27, 32, 33, 35, 52, 55, 57, 72, 75, 77, 112, 115, 117, 132, 133, 135, 172, 175, 177, 192, 195, 213, 217, 219, 222, 225, 231, 232, 235, 237, 243, 247, 252, 253, 255, 259, 261, 267, 272, 273, 275, 279, 289, 292, 295, 297, 312, 315, 319, 322, 323, 325

Offset: 1

Author

Joseph L. Pe, Jan 15 2002

Keywords

• base
• easy
• nonn

Examples

			72 is the concatenation of primes 7 and 2. 132 is the concatenation of primes 13 and 2. 225 is the concatenation of 2, 2 and 5.
		

Links

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

Crossrefs

Cf. A121609.

Programs

Maple

ccat:= proc(m,n) 10^(1+ilog10(n))*m+n end proc:
C[1]:= {2,3,5,7}: P[1]:=C[1]:
for n from 2 to 3 do
  P[n]:= select(isprime, {seq(i,i=10^(n-1)+1..10^n-1,2)});
  C[n]:= P[n];
  for m from 1 to n-1 do
    C[n]:= C[n] union {seq(seq(ccat(p,q),p =P[m]),q=C[n-m])};
  od
od:
seq(op(sort(convert(remove(isprime,C[n]),list))),n=1..3); # Robert Israel, Jan 22 2020

PARI

for(n=1,999, !isprime(n) && is_A152242(n) && print1(n", ")) \\ M. F. Hasler, Oct 16 2009

Formula

A066737 = A152242 \ A000040 = A152242 intersect A002808. - M. F. Hasler, Oct 16 2009

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), Apr 03 2002

Missing terms added by M. F. Hasler, Oct 16 2009