login
Natural numbers which are not odd primes: composites plus 1 and 2.
19

%I #23 Jul 14 2024 08:31:07

%S 1,2,4,6,8,9,10,12,14,15,16,18,20,21,22,24,25,26,27,28,30,32,33,34,35,

%T 36,38,39,40,42,44,45,46,48,49,50,51,52,54,55,56,57,58,60,62,63,64,65,

%U 66,68,69,70,72,74,75,76,77,78,80,81,82,84,85,86,87,88,90,91,92,93,94

%N Natural numbers which are not odd primes: composites plus 1 and 2.

%H Harry J. Smith, <a href="/A065090/b065090.txt">Table of n, a(n) for n = 1..1000</a>

%F A151763(a(n)) = 0.

%o (PARI) { n=0; for (m=1, 10^9, if (!isprime(m) || m==2, write("b065090.txt", n++, " ", m); if (n==1000, return)) ) } \\ _Harry J. Smith_, Oct 06 2009

%o (Haskell)

%o import Data.List (elemIndices)

%o a065090 n = a065090_list !! (n-1)

%o a065090_list = map (+ 1) $ elemIndices 0 a151763_list

%o -- _Reinhard Zumkeller_, Oct 06 2011

%o (Python)

%o from sympy import composite

%o def A065090(n): return composite(n-2) if n>2 else n # _Chai Wah Wu_, Jul 13 2024

%Y Cf. A002808, A006005.

%Y Complement of A065091.

%K nonn,easy

%O 1,2

%A _Labos Elemer_, Nov 12 2001