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 A216169 Composite numbers > 9 which yield a prime whenever a 0 is inserted between any two digits. 13
 49, 119, 121, 133, 161, 169, 203, 253, 299, 301, 319, 323, 403, 407, 473, 493, 511, 539, 551, 581, 611, 667, 679, 713, 869, 901, 913, 943, 1007, 1067, 1079, 1099, 1211, 1273, 1691, 1729, 1799, 1909, 2021, 2047, 2101, 2117, 2359, 2407, 2533, 2717, 2759, 2899 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Paolo P. Lava and Giovanni Resta, Table of n, a(n) for n = 1..10000 (first 1500 terms from Paolo P. Lava) EXAMPLE 2359 is not prime but 23509, 23059 and 20359 are all primes. MAPLE A216169:=proc(q, x) local a, b, c, i, n, ok; for n from 10 to q do if not isprime(n) then   a:=n; b:=0; while a>0 do b:=b+1; a:=trunc(a/10); od; a:=n; ok:=1;   for i from 1 to b-1 do c:=a+9*10^i*trunc(a/10^i)+10^i*x;     if not isprime(c) then ok:=0; break; fi; od;   if ok=1 then print(n); fi; fi; od; end: A216169(1000, 0); MATHEMATICA Select[Range[10, 3000], CompositeQ[#]&&AllTrue[Table[FromDigits[ Insert[ IntegerDigits[ #], 0, n]], {n, 2, IntegerLength[#]}], PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Mar 13 2018 *) PROG (PARI) is(n, L=logint(n+!n, 10)+1, P)={!isprime(n) && !for(k=1, L-1, isprime([10*P=10^(L-k), 1]*divrem(n, P))||return) && n>9} \\ M. F. Hasler, May 10 2018 CROSSREFS Subset of composite numbers in A164329. - M. F. Hasler, May 10 2018 Cf. A068673, A068674, A068677, A068679, A069246, A215417, A215419-A215421, A216165-A216168. Sequence in context: A088868 A044236 A044617 * A090095 A163245 A084733 Adjacent sequences:  A216166 A216167 A216168 * A216170 A216171 A216172 KEYWORD nonn,base AUTHOR Paolo P. Lava, Sep 03 2012 EXTENSIONS Name edited by M. F. Hasler, May 10 2018 STATUS approved

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Last modified October 23 06:48 EDT 2019. Contains 328335 sequences. (Running on oeis4.)