a puxxle

[N. J. A. Sloane]

Dear Seqfans:
Someone just sent this in.  I gave it an A-number.  But I can't
add it to the OEIS until the missing term is filled in. Any ideas?
The differences are suggestive

%I A117713
%S A117713 1,3,8,18,__,89,189
%N A117713 This sequence was a question on a civil service test a friend of mine took. They had to fill in the blank number. Is there an answer to this??.
%O A117713 0,2
%K A117713 nonn
%A A117713 Louis Ciotti (lciotti(AT)twcny.rr.com), Apr 13 2006

Differences: 2 5 10 a b 100 , but a+b = 71, which is ugly.

Neil