a puxxle

[hv at crypt.org]

"N. J. A. Sloane" <njas at research.att.com> wrote:
: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.

This makes me think of coins: UK has 1, 2, 5, 10, 20, 50, 100, 200; first
sums would give 1, 3, 8, 18, 38, 88, 188, 388 which is close, but I can't
see a good reason to add an extra penny for the last 3 or 4 values.
Without that, it could be defined as "least amount (in pence) that can be
made with n distinct UK coins".

If I was doing the test I'd guess at 38 and cross my fingers.

Hugo