9/11, two numbers that conjure huge emotional resonance.
The al-Qaeda terrorist attacks of Tuesday September 11 2001 - on the World Trade Centre in New York and Pentagon in Virginia - was witnessed by many, many millions who were glued to TVs around the globe.
The overwhelming, barbaric, futility of 9/11 tends to be the abiding memory for those who suffered, helpless, throughout that fateful day.
A counterbalance to the horror of 9/11 is therefore to be welcomed and Come From Away delivers this during a memorable musical evening in the theatre.
Come From Away, which is winner of four Olivier Awards including Best New Musical, focuses on the consequences of US airspace being locked down with 38 planes ordered to land in the small Canadian town of Gander, Newfoundland.
Some 7,000 passengers and crew needed looking after, in the most traumatic of circumstances, and the community joined as one to provide food, shelter and comfort for those stranded.
Irene Sankoff and David Hein, the musicals creators, went to Gander on the 10th anniversary of 9/11 to hear and record what was a spontaneous outpouring of kindness by its residents.
The resulting musical was originally intended to be a performed as a high school theatre project but it was soon obvious this story deserved a far wider audience.
The musical had runs in Seattle, Washington DC and Toronto before opening on Broadway in 2017, where it won seven Tony Awards including Best Musical.
It is currently playing to London West End audiences at the Phoenix Theatre.
This is an ensemble musical with every performer and musician integral to providing what is a genuinely joyful and very moving evening in the theatre.
There are no stand out performances, but then nor should there be.
This is as much a collective success, by all performers and musicians, as was that achieved by the folk of Ganger.
The staging is simple but this makes it all the more effective as the cast switch roles (and tables and chairs) to provide a real insight into the trauma, tribulation and ultimate triumph that can emerge from adversity.
The excellent musicians play an essential and integrated onstage role in keeping up the pace of the production.
Finally, there are the many personal vignettes weaved into Come From Away that bring us closer and ever more intimately into the lives of people brought together in adversity.
It all leads to a finale that was tearfully heartening.
Come From Away is a wonderfully warm evening of musical theatre and a reaffirming recognition that the vast majority of people on this planet are good people.