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

1,1

Links

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

Example

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.

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 *)

Crossrefs

Cf. A000040, A003808, A141468, A155030.

Sequence in context: A268492 A130112 A019348 * A191068 A069690 A037003

Adjacent sequences: A155022 A155023 A155024 * A155026 A155027 A155028

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Jan 19 2009

Extensions

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

Status

approved