A064143 - OEIS

%I #13 Dec 14 2024 14:42:55

%S 0,2,3,5,7,5,12,14,9,7,23,21,27,27,29,31,48,46,62,60,59,59,81,79,66,

%T 66,59,59,93,93,124,126,120,118,125,123,141,141,158,156,193,193,225,

%U 225,194,194,243,241,241,241,245,245,298,298,321,321,314,314,365,365,395

%N Sum of unitary prime divisors of binomial(n, floor(n/2)).

%H Harry J. Smith, <a href="/A064143/b064143.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A063956(A001405(n)).

%o (PARI) a(n) = { my(f=factor(binomial(n, n\2))); sum(i=1, #f~, if (f[i,2]==1, f[i,1])) } \\ _Harry J. Smith_, Sep 09 2009

%Y Cf. A001405, A008472, A034444, A056169, A063956.

%K nonn

%O 1,2

%A _Labos Elemer_, Sep 11 2001