A095208 n if n is composite else 10*n.

10, 20, 30, 4, 50, 6, 70, 8, 9, 10, 110, 12, 130, 14, 15, 16, 170, 18, 190, 20, 21, 22, 230, 24, 25, 26, 27, 28, 290, 30, 310, 32, 33, 34, 35, 36, 370, 38, 39, 40, 410, 42, 430, 44, 45, 46, 470, 48, 49, 50, 51, 52, 530, 54, 55, 56, 57

Offset: 1

Author

Amarnath Murthy, Jun 07 2004

Keywords

• easy
• less
• nonn

Comments

In base 10 the smallest composite number starting with the same digits as n.

The average of the first n terms is n/2 + 9n/(2 log n) + O(n log log n/log^2 n). - Charles R Greathouse IV, Jun 08 2015

Examples

			4 is composite, therefore a(4) = 4. 5 is prime, hence a(5) = 50.
		

Crossrefs

Cf. A018800.

Programs

Mathematica

f[n_] := If[PrimeQ[n] || n == 1, 10 n, n]; Array[f, 57] (* Robert G. Wilson v, Jul 05 2011 *)
Array[If[CompositeQ[#],#,10#]&,60] (* Harvey P. Dale, Jan 24 2015 *)

PARI

a(n)=if(isprime(n),10*n,if(n>1,n,10)) \\ Charles R Greathouse IV, Jun 08 2015

Extensions

Edited and extended by Stefan Steinerberger, Jun 15 2007

Edited by Arkadiusz Wesolowski, Jul 05 2011