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A141099 Number of unordered pairs of odd nonprime numbers that sum to 2n. 4

%I

%S 1,0,0,0,1,0,0,1,1,0,1,1,1,1,2,0,2,3,0,2,3,1,2,3,3,2,4,2,3,5,1,4,6,1,

%T 5,5,3,4,7,3,4,7,4,4,9,4,5,8,4,7,9,5,6,8,6,7,10,6,6,13,5,7,13,5,10,11,

%U 8,8,11,9,10,14,9,9,16,7,12,15,8,12,15,9,10,17,14,11,16,12,12,19,11,13,19

%N Number of unordered pairs of odd nonprime numbers that sum to 2n.

%C See A141100 for pairs of odd composite numbers. We have a(n) > 0 except for the 8 values of 2n given in A046458.

%H T. D. Noe, <a href="/A141099/b141099.txt">Table of n, a(n) for n=1..1000</a>

%e a(18)=3 because 36 = 1+35 = 9+27 = 15+21.

%t Table[cnt=0; Do[If[ !PrimeQ[i] && !PrimeQ[2n-i], cnt++ ], {i,1,n,2}]; cnt, {n,100}]

%Y Cf. A141095, A141097.

%K nonn

%O 1,15

%A _T. D. Noe_, Jun 02 2008, Jun 05 2008

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Last modified February 5 23:07 EST 2023. Contains 360091 sequences. (Running on oeis4.)