1. A method comprising: performing operations as follows on a processor of an electronic device: establishing a programmatic association in a one-to-one relationship between mathematical operators and directions of movement that a user can make when selecting number keys among an arrangement of number keys that can be displayed on a display device; receiving a first number from a user selection of a first number key of the arrangement of number keys displayed on the display device; receiving a second number from a user selection of a second number key of the arrangement of number keys; determining a first direction of user movement from the first number key to the second number key; selecting a first mathematical operator among the mathematical operators that is programmatically associated with the first direction; combining the first and second numbers using the first mathematical operator to generate an output number; providing the output number to a secure program to control user access to a protected operation of the secure program; obtaining a security number that allows user access to the protected operation of the secure program; for each of a plurality of digits of the security number, determining a pair of numbers that is combinable using one of the mathematical operators to generate the digit of the security number, and displaying the pair of numbers in an adjacent pair of number keys in the arrangement and with one of the pair of number keys offset from the other one of the pair of numbers keys in a direction that is programmatically associated with the one of the mathematical operators.