cp's OEIS Frontend

A064916 a(n) = n/lpf(n) + lpf(n) - 1, where lpf = A020639 = least prime factor.

%I A064916 #16 Jun 19 2018 05:14:23
%S A064916 2,3,3,5,4,7,5,5,6,11,7,13,8,7,9,17,10,19,11,9,12,23,13,9,14,11,15,29,
%T A064916 16,31,17,13,18,11,19,37,20,15,21,41,22,43,23,17,24,47,25,13,26,19,27,
%U A064916 53,28,15,29,21,30,59,31,61,32,23,33,17,34,67,35,25,36,71,37,73,38,27
%N A064916 a(n) = n/lpf(n) + lpf(n) - 1, where lpf = A020639 = least prime factor.
%C A064916 a(n) = A032742(n) + A020639(n) - 1; a(n) <= n and for n > 1 a(n) = n iff n is prime.
%H A064916 Harvey P. Dale, <a href="/A064916/b064916.txt">Table of n, a(n) for n = 2..1001</a>
%e A064916 a(18) = 18/2 + 2 - 1 = 10;
%e A064916 a(19) = 19/19 + 19 - 1 = 19.
%t A064916 lpf[n_]:=Module[{lp=FactorInteger[n][[1,1]]},n/lp+lp-1]; Array[lpf, 80, 2] (* _Harvey P. Dale_, Sep 25 2011 *)
%o A064916 (PARI) lpf(n)= { local(f); f=factor(n); return(f[1, 1]) } { for (n=2, 1000, L=lpf(n); a=n / L + L - 1; write("b064916.txt", n, " ", a) ) } \\ _Harry J. Smith_, Sep 28 2009
%o A064916 (PARI) a(n) = my(p = vecmin(factor(n)[,1])); n/p + p - 1; \\ _Michel Marcus_, Jun 19 2018
%Y A064916 Cf. A064920, A064917, A064918, A032742, A020639, A064919.
%K A064916 nonn
%O A064916 2,1
%A A064916 _Reinhard Zumkeller_, Oct 14 2001