The most common and most likely answer to this crossword clue is the 7 plus 4 plus 6 letter word PENNIES FROM HEAVEN
I've seen this crossword clue in The Times
P
E
N
N
I
E
S
F
R
O
M
H
E
A
V
E
N
More clues leading to the result PENNIES FROM HEAVEN
Buddy explains!
The straight part
We know that "number" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case number = pennies from heaven.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.