Randon Number Selection formula that excludes previously selected number

one way
for 3 separate from 27 to 29
a1=RANDBETWEEN(27,29)
b1 =IF(A1=27,CHOOSE(RANDBETWEEN(1,2),28,29),IF(A1=28,CHOOSE(RANDBETWEEN(1,2),27,29),IF(A1=29,CHOOSE(RANDBETWEEN(1,2),27,28))))
c1=84-SUM(A1:B1)

First Random
=INDEX({27;28;29},RANDBETWEEN(1,3))

Second Random
=SMALL(INDEX(({27;28;29}<>C11)*({27;28;29}),0,0),RANDBETWEEN(2,3))

Last
=SUMPRODUCT(({27;28;29}<>C11)*({27;28;29}<>E11)*({27;28;29}))

in that case ,i like the second one but
c11=RANDBETWEEN(27,29)
d11 =SMALL(INDEX(({27;28;29}<>C11)*({27;28;29}),0,0),RANDBETWEEN(2,3))
=84-SUM(C11:D11)
would be shorter

Awesome! That's my very first successful use of INDEX to 'float' an array.

Or this.....

A1 =CHOOSE(RANDBETWEEN(1,3),27,28,29)
B1 =CHOOSE(MATCH(TRUE,INDEX({27,28,29}<>A1,0),0),27,28,29)
C1 =84-SUM(A1:B1)

@sktneer
that doesnt give a random second number
=CHOOSE(MATCH(TRUE,INDEX({27,28,29}<>A2,0),0),27,28,29) will always give 27 if a1 is 28 or 29

My initial attempt was to find the first not-match, and randomly choose between that and a BigNum Lookup which pulls the last not-match.

84-SUM is so brilliant. I feel so humbled by its simplicity.