

A095208


n if n is composite else 10*n.


0



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
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OFFSET

1,1


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


LINKS

Table of n, a(n) for n=1..57.


EXAMPLE

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


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 *)


PROG

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


CROSSREFS

Cf. A018800.
Sequence in context: A242964 A063117 A157938 * A291625 A172260 A300024
Adjacent sequences: A095205 A095206 A095207 * A095209 A095210 A095211


KEYWORD

easy,less,nonn


AUTHOR

Amarnath Murthy, Jun 07 2004


EXTENSIONS

Edited and extended by Stefan Steinerberger, Jun 15 2007
Edited by Arkadiusz Wesolowski, Jul 05 2011


STATUS

approved



