Why, when i search in "Calc" it shows me "7461778888" and "A7461778888" ? These are not the same obviously.

LibreOffice Calc

Btw, please don’t start questions as wiki, see also Please add deprecation message to "community wiki" checkbox for why.

If you want to search for an exact string, not any part of a cell content, then check the Entire cells box (assuming you’re talking of the Find&Replace dialog).