A155030 Primes p=A000040(n) with prime index n such that the concatenation n//p is a composite number.

5, 11, 17, 31, 41, 67, 109, 127, 157, 191, 211, 241, 277, 331, 367, 401, 461, 509, 547, 563, 587, 599, 617, 739, 773, 797, 859, 877, 919, 967, 991, 1031, 1063, 1087, 1153, 1171, 1201, 1217, 1297, 1409, 1447, 1471, 1499, 1523, 1597, 1621, 1669, 1723, 1741

Offset: 1

Author

Juri-Stepan Gerasimov, Jan 19 2009

Keywords

• nonn
• base

Comments

Demanding that the index is not a prime would lead to A155025 instead.

Examples

			For the index n=3, a prime, p = prime(3)=5, the concatenation 35 is composite, so p=5 is added to the sequence.
For the index n=5, a prime, p = prime(5)=11, the concatenation 511 is composite, so p=11 is added to the sequence.
For the index n=6, not a prime, nothing is added to the sequence.
For the index n=7, a prime, p = prime(7)=17, the concatenation 717 is composite, so p=17 is added to the sequence.
		

Crossrefs

Cf. A000027, A000040, A002808, A155025.

Programs

Mathematica

Prime[#]&/@Select[Prime[Range[70]],CompositeQ[FromDigits[Join[ IntegerDigits[ #], IntegerDigits[ Prime[#]]]]]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 14 2019 *)

Extensions

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