A064788 - OEIS

%I #17 Dec 01 2017 03:01:13

%S 1,2,5,3,4,8,13,9,6,7,12,18,25,19,14,10,11,17,24,32,41,33,26,20,15,16,

%T 23,31,40,50,61,51,42,34,27,21,22,30,39,49,60,72,85,73,62,52,43,35,28,

%U 29,38,48,59,71,84,98,113,99,86,74,63,53,44,36,37,47,58,70,83,97,112

%N Inverse permutation to A060736.

%H Boris Putievskiy, <a href="http://arxiv.org/abs/1212.2732">Transformations Integer Sequences And Pairing Functions</a>, arXiv:1212.2732 [math.CO], 2012.

%H Eric Weisstein's MathWorld, <a href="http://mathworld.wolfram.com/PairingFunction.html">Pairing functions</a>

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

%F a(n) = (i+j-1)*(i+j-2)/2+j, where i=min(t; t^2-n+1), j=min(t; n-(t-1)^2), t=floor(sqrt(n-1))+1. - _Boris Putievskiy_, Dec 24 2012

%o (PARI) A064788(n)={my(t=sqrtint(n-1)+1); A000217(min(t,t^2-n+1)-2+n=min(t, n-(t-1)^2))+n} \\ recall: A000217(n)=(n+1)*n/2 \\ _M. F. Hasler_, Jan 13 2013

%Y Cf. A064790, A194280.

%K easy,nonn

%O 1,2

%A _N. J. A. Sloane_, Oct 20 2001

%E More terms from _David Wasserman_, Jan 15 2002