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A154967 Nonprime numbers n such that concatenation of n and n-th prime is composite. 1
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 (list; graph; refs; listen; history; text; internal format)
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: A169928 A067683 A164276 * A271211 A072381 A046415

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

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Last modified April 23 02:43 EDT 2019. Contains 322380 sequences. (Running on oeis4.)