Released in 1949, “Grandma Plays The Numbers” was actually one of Blues legend Wynonie Harris' less popular songs in its contemporary time. The song gained modern popularity after being featured in the critically acclaimed 2015 video game Fallout 4.
[Intro]
Say Wynonie, I was by your house last night and guess what happened?
What happened, mon?
Your grandma was playing the numbers
Well you just finding that out?
(Well what do you know, hmm?)
[Chorus]
(We found out) Yes we did
(We found out) Now we know
(We found out) We found out that Grandma plays the numbers
(We found out) Yes we did
(We found out) She couldn't keep it hid
(We found out) Now we know that Grandma plays the numbers
[Verse 1]
Thinks about 'em everyday
Dreams about 'em every night
Gets up early in the morning
See all 'em numbers come down just right
[Chorus]
(We found out) Yes we know
(We found out) Bless her soul
(We found out) Now we know that Grandma plays the numbers
[Interlude]
[Chorus]
(We found out) Yes we know
(We found out) Bless her soul
(We found out) Now we know that Grandma plays the numbers
(We found out) Yes, oh yes
(We found out) We found out
(We found out) Now we know that Grandma plays the numbers
[Verse 2]
She's at the fruit stand everyday
Buys bananas by the bunch
She looks at all the price tags
That's where she gets her hunch
[Chorus]
(We found out) Yes we know
(We found out) Bless her soul
(We found out) Now we know that Grandma plays the numbers
[Outro]
Hey, Grandma, did you get your numbers in yet?
Well, I 'spect I did, son
Well, what did you play?
Three, six, nine
(Well, what do you know?)
Grandma Plays The Numbers was written by Wynonie Harris.
Three, six, nine holds no meaning and was likely selected by Wynonie to resemble a sort of lucky number that Grandma came up with (or perhaps saw at the fruit stand). They are multiples of three and have a sort of pattern. Reddit thread that discusses the numbers