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Inverse permutation to A135764.
8

%I #15 Feb 06 2015 10:36:04

%S 1,3,2,6,4,5,7,10,11,8,16,9,22,12,29,15,37,17,46,13,56,23,67,14,79,30,

%T 92,18,106,38,121,21,137,47,154,24,172,57,191,19,211,68,232,31,254,80,

%U 277,20,301,93,326,39,352,107,379,25,407,122,436,48,466,138,497,28,529,155,562,58,596,173,631,32,667,192,704,69,742,212,781,26,821,233,862,81

%N Inverse permutation to A135764.

%H Antti Karttunen, <a href="/A249725/b249725.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>

%F a(n) = 1 + (((A003602(n)+A007814(n))^2 + A007814(n) - A003602(n))/2).

%F As a composition of other permutations:

%F a(n) = A249742(A249811(n)).

%F a(n) = A246276(A246676(n)).

%F Other identities. For all n >= 0 the following holds:

%F a(A005408(n)) = A000124(n). [Maps odd numbers to central polygonal numbers].

%F a(A000079(n)) = A000217(n+1). [Maps powers of two to triangular numbers].

%o (Scheme) (define (A249725 n) (+ 1 (* (/ 1 2) (+ (expt (+ (A003602 n) (A007814 n)) 2) (- (A003602 n)) (A007814 n)))))

%o (PARI) a(n) = {r = 1; while(!(n%2), n = n >> 1; r++); k = 1 + n \ 2; binomial(r + k - 1, 2) + r} \\ _David A. Corneth_, Feb 05 2015

%Y Inverse: A135764.

%Y Similar or related permutations: A209268, A246276, A246676, A249742, A249811.

%Y Cf. A000079, A000124, A000217, A003602, A005408, A007814.

%K nonn

%O 1,2

%A _Antti Karttunen_, Nov 15 2014