A309529 Start with a(1)=2; thereafter the sequence is always extended by adding the n-th digit of the sequence to a(n) if a(n) is even, else subtracting it.

2, 4, 8, 16, 17, 11, 10, 17, 16, 17, 16, 16, 17, 10, 11, 5, 4, 11, 10, 16, 17, 11, 10, 17, 16, 16, 17, 16, 21, 17, 16, 17, 16, 16, 17, 11, 10, 17, 16, 17, 16, 16, 17, 10, 11, 5, 4, 10, 11, 4, 5, -1, -3, -4, -3, -10, -9, -15, -16, -9, -10, -4, -3, -9, -10

Offset: 1

Author

Eric Angelini and Jean-Marc Falcoz, Aug 06 2019

Keywords

• sign
• base

Comments

Among the first 10^8 terms, the last positive value occurs at n=28823742. - Lars Blomberg, Aug 10 2019

Examples

			The sequence begins with 2,4,8,16,17,11,10,17,...
As a(1) = 2 (even), we have a(2) = a(1) + [the 1st digit of the seq] = 2 + 2 = 4;
as a(2) = 4 (even), we have a(3) = a(2) + [the 2nd digit of the seq] = 4 + 4 = 8;
as a(3) = 8 (even), we have a(4) = a(3) + [the 3rd digit of the seq] = 8 + 8 = 16;
as a(4) = 16 (even), we have a(5) = a(4) + [the 4th digit of the seq] = 16 + 1 = 17;
as a(5) = 17 (odd), we have a(6) = a(5) - [the 5th digit of the seq] = 17 - 6 = 11;
as a(6) = 11 (odd), we have a(7) = a(6) - [the 6th digit of the seq] = 11 - 1 = 10;
etc.
		

Links

• Jean-Marc Falcoz, Table of n, a(n) for n = 1..42917
• Lars Blomberg, Graph of 10^8 terms
• Lars Blomberg, Graph of accumulated sums of 10^8 terms

Crossrefs

Cf. A309521 (same idea, but dealing with primes instead of even numbers).