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 A066737 Composite numbers that are concatenations of primes. 4
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 FORMULA A066737 = A152242 \ A000040 = A152242 intersect A002808. - M. F. Hasler, Oct 16 2009 EXAMPLE 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. 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 PROG (PARI) for(n=1, 999, !isprime(n) && is_A152242(n) && print1(n", ")) \\ M. F. Hasler, Oct 16 2009 CROSSREFS Cf. A121609. Sequence in context: A186780 A034304 A167459 * A121609 A092631 A061371 Adjacent sequences:  A066734 A066735 A066736 * A066738 A066739 A066740 KEYWORD base,easy,nonn AUTHOR Joseph L. Pe, Jan 15 2002 EXTENSIONS More terms from Larry Reeves (larryr(AT)acm.org), Apr 03 2002 Missing terms added by M. F. Hasler, Oct 16 2009 STATUS approved

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Last modified January 26 09:21 EST 2021. Contains 340435 sequences. (Running on oeis4.)