Is it possible to restrict user to input certain data without refering to another cell?

[Yo1485]

I want to restrict user from entering alphabets like I,O,Q and S in a cell. Can we do this using data validation or any formula because I don't wan't to use drop-down list or refer to values in other cells either.

[kspeese]

If you want numbers only, how about you do data validation. Then select whole number and use the criteria "Greater Than or Equal to" and select 0.

[benishiryo]

welcome to the forum. is it case sensitive? like if it's
q
is it accepted?

is 1 single letter not allowed or none of those letters can be found? eg
abQc
is it accepted?

select the cells you want the dropdown applied to (say A1:B5). go to Data -> Data Validation -> Allow: Custom-> Formula:
non-case sensitive & none of the letters can be found:
=COUNTIF(A1,"*I*")+COUNTIF(A1,"*O*")+COUNTIF(A1,"*Q")+COUNTIF(A1,"*S*")=0

none-case sensitive & single letter:
=AND(A1<>"I",A1<>"O",A1<>"Q",A1<>"S")

case-sensitive & none of the letters can be found
=AND(ISERR(FIND("I",A1)),ISERR(FIND("O",A1)),ISERR(FIND("Q",A1)),ISERR(FIND("S",A1)))

[Yo1485]

Thank you benishiryo for the welcome and also for the prompt solution. Its exactly what I wanted and works fine for me. Sorry for providing less information, yes its only single letter and non-case sensitive