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a(n) is the least number k such that A066323(k) = n.
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%I #23 Jan 14 2023 16:52:14

%S 0,1,2,3,4,5,6,7,23,39,55,71,87,103,359,615,871,1127,1383,1639,5735,

%T 9831,13927,18023,22119,26215,91751,157287,222823,288359,353895,

%U 419431,1468007,2516583,3565159,4613735,5662311,6710887,23488103,40265319,57042535,73819751

%N a(n) is the least number k such that A066323(k) = n.

%C a(n) is the least number k whose sum of digits in base i-1 (or in base -4) is n.

%H Amiram Eldar, <a href="/A342728/b342728.txt">Table of n, a(n) for n = 0..1000</a>

%H Walter Penney, <a href="http://dx.doi.org/10.1145/321264.321274">A "binary" system for complex numbers</a>, Journal of the ACM, Vol. 12, No. 2 (1965), pp. 247-248.

%H <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,16,-16).

%F a(n) = n for n <= 7, and a(n) = a(n-1) + 16*a(n-6) - 16*a(n-7) for n > 7.

%F G.f.: x*(1 + x + x^2 + x^3 + x^4 + x^5 - 15*x^6)/(1 - x - 16*x^6 + 16*x^7). - _Stefano Spezia_, Mar 20 2021

%F From _Greg Dresden_, Jun 21 2021: (Start)

%F a(3*n+1) = (24 + (4^n)*(25 - 9*(-1)^n))/40.

%F a(3*n+2) = (24 + (4^n)*(50 + 6*(-1)^n))/40.

%F a(3*n+3) = (24 + (4^n)*(75 + 21*(-1)^n))/40. (End)

%t Join[{0}, LinearRecurrence[{1,0,0,0,0,16,-16}, Range[7], 50]]

%Y Cf. A007608, A066321, A066323, A271472, A342725, A342726, A342727, A342729.

%K nonn,base,easy

%O 0,3

%A _Amiram Eldar_, Mar 19 2021