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A187743 Smallest number which is an unordered sum of two odd abundant numbers in exactly n ways. 1

%I #13 Jan 03 2013 16:02:19

%S 1890,3150,4410,5670,6930,8190,9450,10710,11970,12600,14490,13860,

%T 15750,17010,20160,19530,22050,20790,23940,24570,26460,28350,28980,

%U 64680,27720,32130,32760,38430,39690,40320,34650,51660,53550,56700,41580,58590,48510,70560

%N Smallest number which is an unordered sum of two odd abundant numbers in exactly n ways.

%C The first 10000 terms are all divisible by 210.

%H Donovan Johnson, <a href="/A187743/b187743.txt">Table of n, a(n) for n = 1..10000</a>

%e Summands are odd abundant numbers.

%e a(1) = 1890 = 945 + 945.

%e a(2) = 3150 = 945 + 2205 = 1575 + 1575.

%e a(3) = 4410 = 945 + 3465 = 1575 + 2835 = 2205 + 2205.

%e a(4) = 5670 = 945 + 4725 = 1575 + 4095 = 2205 + 3465 = 2835 + 2835.

%o (PARI) /* finds first 1000 terms */ mx=4616430; ct=vector(mx); k=9384; v=vector(k); n=vector(1000); c=0; forstep(i=945, mx-1, 2, if(sigma(i)-2*i>0, c++; v[c]=i)); for(i=1, k, for(j=i, k, s=v[i]+v[j]; if(s<=mx, ct[s]++, next(2)))); forstep(i=1890, mx, 2, if(ct[i]>0 && ct[i]<=1000 && n[ct[i]]==0, n[ct[i]]=i)); for(i=1, 1000, write("b187743.txt", i " " n[i]))

%Y Cf. A005231, A168226.

%K nonn

%O 1,1

%A _Donovan Johnson_, Jan 03 2013

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