There are several idioms formed with numbers. Check them out!

Cero

ser un cero a la izquierda – to be useless

Uno

una y no más, Santo Tomás – once is enough

Dos

cada dos por tres – very frequently
estar entre dos fuegos – to be caught in the crossfire
estar entre dos aguas – to sit on the fence
estar a dos velas – to be without something (money, sex)
como dos y dos son cuatro – as sure as eggs is eggs

Tres

dar tres cuartos al pregonero – to let a secret out
buscar tres pies al gato – to make things more complicated than they are
donde Cristo dio las tres voces – in a very distant, solitary place
A la tercera va la vencida – third time lucky
Ni a la de tres – Nothing doing!
no ver tres en un burro – to see nothing (because it is so dark)

Cuatro

echar un cuarto a espadas – to intervene, give an opinion
estar a la cuarta pregunta – to be pennyless
Estaban/había cuatro gatos. – There were very few people ther

Cinco

Choca esos cinco – Give me five!

Siete

hacerse un siete en la ropa – to have a tear your clothes
estar en el séptimo cielo – to be in seventh heaven
andar/recorrer las siete partidas – to keep going over (an idea)
tener siete vidas – to have nine lives
pícaro de siete suelas – helluva rascal

Diez

hacer las diez de últimas – to end up with nothing

Once

meterse en camisa de once varas – to poke your nose in (where it is not your concern)

trece
mantenerse en sus trece – to stick to your guns
martes y trece – Tuesday the thirteenth (considered an unlucky day, like Friday the thirteenth in the English-speaking world)

Cuarenta

cantarle las cuarenta – to give someone a piece of your mind

Cien

poner a uno a cien – to (cause to) get in a state of high excitement
Dentro de cien años todos calvos. – in the future it won’t matter

Mil, millón

Mil gracias /Un millón de gracias – Many thanks
Vendrá a las mil quinientas. – He’ll come well beyond the agreed time.

Nos vemos prontito!