A154967 Nonprime numbers n such that concatenation of n and n-th prime is composite.

1, 8, 9, 10, 14, 15, 16, 20, 21, 22, 24, 25, 26, 28, 32, 33, 34, 38, 39, 40, 44, 48, 49, 50, 51, 52, 55, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 84, 86, 87, 88, 90, 91, 94, 95, 96, 98, 100, 102, 104, 105, 106, 108, 110, 111, 112, 114, 116, 118

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

The concatenation of the nonprime 1 and the first prime 2 is the composite 12, hence 1 is in the sequence.
Concatenation of nonprime 9 and ninth prime 23 is the composite 923 = 13*71, hence 9 is in the sequence.

Mathematica

Select[Range[120], !PrimeQ[#]&&CompositeQ[FromDigits[Join[ IntegerDigits[ #], IntegerDigits[ Prime[#]]]]]&] (* Harvey P. Dale, Mar 08 2018 *)

Prog

(Magma) [ n: n in [1..118] | not IsPrime(n) and not IsPrime(StringToInteger(IntegerToString(n) cat IntegerToString(NthPrime(n)))) ];

Crossrefs

Cf. A000040 (primes), A002808 (composites), A018252 (nonprime numbers).

Sequence in context: A338026 A359881 A164276 * A271211 A341044 A072381

Adjacent sequences: A154964 A154965 A154966 * A154968 A154969 A154970

Keyword

nonn,base,easy,less

Author

Juri-Stepan Gerasimov, Jan 18 2009

Extensions

Edited and extended beyond a(12) by Klaus Brockhaus, Jan 20 2009

Status

approved