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%I #5 Nov 05 2016 07:23:20
%S 1,3,2,10,4,5,6,36,9,8,28,14,15,21,7,136,11,27,120,19,91,105,20,44,45,
%T 55,13,78,35,12,66,528,77,17,496,90,435,465,43,53,325,351,54,406,18,
%U 65,378,152,153,171,16,210,135,34,190,300,26,119,276,25,231,253,104,2080,118,275,2016,32,1891,1953,252,324,1653,1711,33
%N Inverse permutation to A277820.
%H Antti Karttunen, <a href="/A277821/b277821.txt">Table of n, a(n) for n = 1..16383</a>
%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%F a(n) = (1/2) * ((c+r)^2 - r - 3*c + 2), where c = A277818(n), and r = A268671(n).
%o (Scheme)
%o (define (A277821 n) (let ((row (A268671 n)) (col (A277818 n))) (* (/ 1 2) (- (expt (+ row col) 2) row col col col -2))))
%Y Inverse: A277820.
%Y Cf. A268671, A277818.
%K nonn
%O 1,2
%A _Antti Karttunen_, Nov 03 2016
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