The database has been compiled by David Wilson (davidwwilson(AT)comcast.net) and discussed on the seqfan mailing list, which is related to OEIS. I have added a little html to help browsing.

An addition chain for n is a finite increasing sequence of positive integers whose first element is 1, last element is n, and every element after the first is the sum of two previous elements in the chain. For example:

(1 2 4 5 8 10 13)

is an addition chain for 13. A shortest addition chain for n is an addition chain for n with the smallest possible number of elements. For example,

(1 2 3 6 12 13)

is a shortest addition chain for 13, since there is no addition chain
for 13 with fewer than 6 elements.A Brauer chain is an addition chain in which every member after the first is the sum of the immediately preceeding element and a previous element (possibly the same element). For example,

(1 2 3 6 7 13)

is a Brauer chain for 13.A non-Brauer chain for n is an addition chain for n which is not a Brauer chain. For example

(1 2 4 5 8 13)

is a non-Brauer chain for 13.The single uncompressed acNNNN.txt files can be browsed following these links:

The file acIndx.txt includes summary statistics for the shortest addition chains for n. It can be viewed also as a big table in this separate page. The lines are sorted on n, and have the format

n siz act bct cct

where

n = last element of addition chain

siz = number of elements in shortest addition chain for n

act = number of non-Brauer shortest addition chains for n

bct = number of Brauer shortest addition chains for n

cct = act+bct = total number of shortest addition chains for n

The file ac****.txt, where **** is a zero-padded number n, records all shortest addition chains for n. For example, ac0137.txt records all shortest addition chains for n = 137. Each line describes one of the shortest addition chains for n. Lines are sorted in lexicographic order on the chain elements. The format of each line is

a_1 = first element of chain

a_2 = second element of chain

a_3 = third element of chain

...

a_siz = last element of chain

type = a for non-Brauer chain, b for Brauer chain