A309216 a(0)=0; thereafter a(n) = a(n-1)+n if the (n-1)st digit of the sequence is even, otherwise a(n) = a(n-1)-n.

0, 1, -1, -4, 0, 5, -1, -8, 0, 9, -1, -12, -24, -11, 3, 18, 2, -15, -33, -52, -32, -11, -33, -56, -80, -105, -131, -104, -132, -103, -133, -164, -196, -229, -263, -228, -192, -155, -193, -154, -194, -235, -277, -320, -364, -319, -273, -320, -368, -319, -369, -318, -370, -423, -477, -532

Offset: 0

Author

N. J. A. Sloane, Aug 10 2019

Keywords

• sign
• base

Comments

The absolute values of the digits are 0, 1, 1, 4, 0, 5, 1, 8, 0, 9, 1, 1, 2, 2, 4, 1, 1, 3, 1, 8, 2, 1, 5, 3, 3, 5, 2, ... (Of course the signs can be ignored when looking at the parity of the digits.)

Links

• N. J. A. Sloane, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A003816, A309529, A309214, A309215, A309217.

Programs

Maple

t:=0;
a:=[0]; b:=[]; M:=100;
for i from 1 to M do
v1:=convert(abs(t),base,10); L:=nops(v1);
v2:=[seq(v1[L-i+1],i=1..L)];
b:=[op(b),op(v2)];
if (b[i] mod 2) = 0 then t:=t+i else t:=t-i; fi;
a:=[op(a),t];
od:
a;