

A071904


Odd composite numbers.


24



9, 15, 21, 25, 27, 33, 35, 39, 45, 49, 51, 55, 57, 63, 65, 69, 75, 77, 81, 85, 87, 91, 93, 95, 99, 105, 111, 115, 117, 119, 121, 123, 125, 129, 133, 135, 141, 143, 145, 147, 153, 155, 159, 161, 165, 169, 171, 175, 177, 183, 185, 187, 189, 195
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OFFSET

1,1


COMMENTS

Same as A014076 except for the initial term 1 (which is not a composite number).
Values of quadratic form (2x + 3)*(2y + 3) = 4xy + 6x + 6y + 9 for x, y >= 0.  Anton Joha, Jan 21 2001
Intersection of A002808 and A005408; A000035(a(n))*(1A010051(a(n))) = 1; A020639(a(n)) = A162022(n). [Reinhard Zumkeller, Oct 10 2011]
Composite numbers n such that (n1)^(n1) == 1 (mod n). [Michel Lagneau, Feb 18 2012]


LINKS

Zak Seidov and K. D. Bajpai, Table of n, a(n) for n = 1..10000 (first 1000 terms from Zak Seidov)


FORMULA

a(n) ~ 2n.  Charles R Greathouse IV, Jul 02 2013


EXAMPLE

45 is in the sequence because it is odd and composite (45 = 3 * 3 * 5).
195 is in the sequence because it is odd and composite (195 = 3 * 5 * 13).


MATHEMATICA

Select[Table[n, {n, 9, 300, 2}], !PrimeQ[#] &] (* Vladimir Joseph Stephan Orlovsky, Apr 16 2011 *)
With[{upto = 200}, Complement[Range[9, upto, 2], Prime[Range[ PrimePi[ upto]]]]] (* Harvey P. Dale, Jan 24 2013 *)


PROG

(Haskell)
a071904 n = a071904_list !! (n1)
a071904_list = filter odd a002808_list
 Reinhard Zumkeller, Oct 10 2011
(PARI) is(n)=n%2 && !isprime(n) && n > 1 \\ Charles R Greathouse IV, Nov 24 2012


CROSSREFS

Cf. A002808.
Sequence in context: A079364 A160666 A039769 * A014076 A067800 A155474
Adjacent sequences: A071901 A071902 A071903 * A071905 A071906 A071907


KEYWORD

nice,nonn,easy


AUTHOR

Shyam Sunder Gupta, Jun 12 2002


STATUS

approved



