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A306613
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First differences of A063990 (amicable numbers arranged in increasing order).
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0
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64, 900, 26, 1410, 304, 2096, 544, 668, 136, 4376, 112, 1429, 2310, 2701, 1120, 44604, 3908, 64, 103, 2520, 1530, 4939, 3666, 7883, 1097, 11755, 21780, 103, 784, 1003, 15660, 1849, 646, 10866, 15554, 3126, 4416, 64, 4512, 4520, 11356, 5720, 988, 77108, 28080, 10930
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OFFSET
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1,1
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COMMENTS
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a(n) is the difference between the n-th and (n+1)-th amicable numbers when ordered by increasing value.
For 1 <= k <= 8, a(2k-1) is the difference between the larger and the smaller terms of the k-th amicable pair, and for 1 <= k <= 8, a(2k) is the difference between the smaller term of the (k+1)-th pair and the larger term of the k-th pair. Beginning with the 9th pair (63020,76084), the pairs ordered by their first element are no longer adjacent. - Bernard Schott, Mar 09 2019
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LINKS
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FORMULA
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EXAMPLE
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a(2) = amicable(3) - amicable(2) = 1184 - 284 = 900.
a(1) = 284 - 220 = 64 is the difference between the larger and the smaller terms of the first amicable pair.
a(4) = 2620 - 1210 = 1410 is the difference between the smaller term of the third amicable pair and the larger term of the second amicable pair. (End)
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PROG
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(MATLAB)
clear
clc
A = zeros(100000, 1);
parfor n = 1:1:100000
f = find(rem(n, 1:floor(sqrt(n))) == 0);
f = unique([1, n, f, fix(n./f)]);
A(n) = sum(f) - n;
end
D = [];
d = 1;
for a = 1:1:100000
for b = 1:1:100000
if A(a) == b && A(b) == a && a~=b
D(d) = a;
d = d+1;
end
end
end
D
difference = diff(D)
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CROSSREFS
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Cf. A066539 (difference between larger and smaller terms of n-th amicable pair).
Cf. A139228 (first differences of perfect numbers).
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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