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A256639 a(n) is the base-(-10) representation of a(n-1) read in base 10, starting from -1.

%I A256639 #74 Jun 29 2019 03:54:01
%S A256639 -1,19,199,219,399,419,599,619,799,819,999,19019,21199,39219,41399,
%T A256639 59419,61599,79619,81799,99819,1901999,2118019,3922199,4138219,
%U A256639 5942399,6158419,7962599,8178619,9982799,190198819,211802999,392217019,413823199,594237219,615843399,796257419,817863599,998277619,19019883799
%N A256639 a(n) is the base-(-10) representation of a(n-1) read in base 10, starting from -1.
%C A256639 Decimal -1 in negadecimal is 19, decimal 19 in negadecimal is 199, decimal 199 in negadecimal is 219, ....
%t A256639 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 A256639 (HP 49G calculator) Given a(n) the program produces a(n+1).
%o A256639 ::
%o A256639   CK1&Dispatch
%o A256639   # FF
%o A256639   ::
%o A256639     Z10_
%o A256639     ZINT -10
%o A256639     FPTR2 ^2LAMBIND
%o A256639     NULL$SWAP
%o A256639     BEGIN
%o A256639     1GETLAM
%o A256639     FPTR2 ^IDIV2
%o A256639     FPTR2 ^DupQIsZero?
%o A256639     ?SKIP
%o A256639     ::
%o A256639       2GETLAM
%o A256639       FPTR2 ^RADDext
%o A256639       SWAP
%o A256639       Z1_
%o A256639       FPTR2 ^RADDext
%o A256639       SWAP
%o A256639     ;
%o A256639     FPTR2 ^Z>S
%o A256639     ROT
%o A256639     &$SWAP
%o A256639     FPTR2 ^DupQIsZero?
%o A256639     UNTIL
%o A256639     ABND
%o A256639     DROP
%o A256639     FPTR2 ^S>Z
%o A256639   ;
%o A256639 ;
%Y A256639 Cf. A039723.
%K A256639 sign,base
%O A256639 1,2
%A A256639 _Gerald Hillier_, Apr 23 2015