%I #74 Jun 29 2019 03:54:01
%S -1,19,199,219,399,419,599,619,799,819,999,19019,21199,39219,41399,
%T 59419,61599,79619,81799,99819,1901999,2118019,3922199,4138219,
%U 5942399,6158419,7962599,8178619,9982799,190198819,211802999,392217019,413823199,594237219,615843399,796257419,817863599,998277619,19019883799
%N a(n) is the base-(-10) representation of a(n-1) read in base 10, starting from -1.
%C Decimal -1 in negadecimal is 19, decimal 19 in negadecimal is 199, decimal 199 in negadecimal is 219, ....
%t negaDecimal[n_] := Mod[NestWhileList[Function[k, (Mod[k, 10]-k)/10], n, # != 0&], 10] // Reverse // Rest // FromDigits; a[1] = -1; a[n_] := a[n] = negaDecimal[a[n-1]]; Array[a, 40] (* _Jean-François Alcover_, Nov 23 2016 *)
%o (HP 49G calculator) Given a(n) the program produces a(n+1).
%o ::
%o CK1&Dispatch
%o # FF
%o ::
%o Z10_
%o ZINT -10
%o FPTR2 ^2LAMBIND
%o NULL$SWAP
%o BEGIN
%o 1GETLAM
%o FPTR2 ^IDIV2
%o FPTR2 ^DupQIsZero?
%o ?SKIP
%o ::
%o 2GETLAM
%o FPTR2 ^RADDext
%o SWAP
%o Z1_
%o FPTR2 ^RADDext
%o SWAP
%o ;
%o FPTR2 ^Z>S
%o ROT
%o &$SWAP
%o FPTR2 ^DupQIsZero?
%o UNTIL
%o ABND
%o DROP
%o FPTR2 ^S>Z
%o ;
%o ;
%Y Cf. A039723.
%K sign,base
%O 1,2
%A _Gerald Hillier_, Apr 23 2015