A162022 - OEIS

%I #16 Aug 01 2024 01:30:04

%S 3,3,3,5,3,3,5,3,3,7,3,5,3,3,5,3,3,7,3,5,3,7,3,5,3,3,3,5,3,7,11,3,5,3,

%T 7,3,3,11,5,3,3,5,3,7,3,13,3,5,3,3,5,11,3,3,3,7,5,3,11,3,5,7,3,13,3,3,

%U 5,3,3,5,13,3,11,3,7,3,5,3,3,5,3,3,7,17,3,5,3,13,7,3,5,3,3,11,3,17,5,3,7,3

%N Smallest prime factor of n-th odd composite integers A071904.

%C Records are for n's such that A071904(n) = squares of primes.

%C a(n) = A020639(A071904(n)). [_Reinhard Zumkeller_, Oct 10 2011]

%H Reinhard Zumkeller, <a href="/A162022/b162022.txt">Table of n, a(n) for n = 1..10000</a>

%e A071904(1)=9, hence a(1)=3, A071904(4)=25, hence a(4)=5.

%t nn=501;With[{ci=Complement[Range[9,nn,2],Prime[Range[PrimePi[nn]]]]}, FactorInteger[ #][[1,1]]&/@ci] (* _Harvey P. Dale_, Nov 30 2012 *)

%o (Python)

%o from sympy import primepi, primefactors

%o def A162022(n):

%o     if n == 1: return 3

%o     m, k = n, primepi(n) + n + (n>>1)

%o     while m != k:

%o         m, k = k, primepi(k) + n + (k>>1)

%o     return min(primefactors(m)) # _Chai Wah Wu_, Jul 31 2024

%Y Cf. A014076, A071904.

%K nonn

%O 1,1

%A _Zak Seidov_, Jun 25 2009

%E Corrected example a(4)=5 Francesco Antoni (francesco_antoni(AT)yahoo.com), Aug 04 2010