A155025 Primes p=A000040(n) with nonprime index n such that the concatenation n//p is a composite number.

2, 19, 23, 29, 43, 47, 53, 71, 73, 79, 89, 97, 101, 107, 131, 137, 139, 163, 167, 173, 193, 223, 227, 229, 233, 239, 257, 281, 293, 307, 311, 313, 317, 337, 347, 349, 359, 373, 379, 383, 389, 397, 409, 419, 433, 443, 449, 457, 463, 467, 491, 499, 503, 521, 541, 557, 569

Offset: 1

Author

Juri-Stepan Gerasimov, Jan 19 2009

Keywords

• nonn
• base

Examples

			For the nonprime n=1, p = prime(n) = 2, the concatenation is 12 is composite, and p is added to the sequence.
For the nonprime n=8, p = prime(8) = 19, the concatenation 819 is composite, and p=19 is added to the sequence.
For the nonprime n=12, p = prime(12) = 37, the concatenation 1237 is prime, so p=37 is not added to the sequence.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A003808, A141468, A155030.

Programs

Mathematica

cnQ[{n_,p_}]:=!PrimeQ[n]&&!PrimeQ[FromDigits[Flatten[ IntegerDigits/@ {n,p}]]]; Transpose[Select[Table[{n,Prime[n]},{n,150}],cnQ]][[2]] (* Harvey P. Dale, Dec 18 2012 *)

Extensions

Definition clarified, sequence extended by R. J. Mathar, Oct 14 2009