%0 Journal Article
%T Partition and sum is fast
%A Steve Butler
%A Ron Graham
%A Richard Stong
%J Mathematics
%D 2015
%I arXiv
%X We consider the following "partition and sum" operation on a natural number: Treating the number as a long string of digits insert several plus signs in between some of the digits and carry out the indicated sum. This results in a smaller number and repeated application can always reduce the number to a single digit. We show that surprisingly few iterations of this operation are needed to get down to a single digit.
%U http://arxiv.org/abs/1501.04067v1