%I #8 Nov 05 2016 07:26:47
%S 1,3,2,6,5,4,10,15,9,8,21,7,28,36,14,45,20,13,55,12,66,78,27,11,91,
%T 105,35,120,44,19,136,153,54,26,171,18,190,210,65,17,231,253,77,276,
%U 90,34,300,16,325,351,104,378,119,43,406,435,135,53,465,25,496,528,152,561,170,64,595,33,630,666,189,24,703,741,209,780,230,76,820,23
%N Inverse permutation to A277880.
%H Antti Karttunen, <a href="/A277881/b277881.txt">Table of n, a(n) for n = 1..16384</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 = A277822(n), and r = A277813(n).
%o (Scheme) (define (A277881 n) (let ((row (A277813 n)) (col (A277822 n))) (* (/ 1 2) (- (expt (+ row col) 2) row col col col -2))))
%Y Inverse: A277880.
%Y Cf. A277813, A277822.
%Y Cf. A028401 (terms at powers of 2).
%K nonn
%O 1,2
%A _Antti Karttunen_, Nov 03 2016