I have made a number of contributions to the Online Encyclopedia of Integer Sequences (OEIS). Below are descriptions of the sequences; click on them to go to the OEIS.

Maximum number of cells in a square n X n grid that can be painted such that no two orthogonally adjacent cells are painted, and that every unpainted cell can be reached from the edge of the grid by a series of orthogonal steps to unpainted cells.

Number of quadrilaterals in a triangular matchstick arrangement of side n.

Heyawake numbers: maximum number of painted cells in an n X n grid, such that no two painted cells are orthogonally adjacent and the unpainted cells form a contiguous area.

Hypotenuse of the smallest Pythagorean triple whose legs are m and 2m + n.

Lowest number of the form 11*m+1 with exactly n prime factors, counted with multiplicity.

Number of button presses required to try every combination of a binary combination lock with n number buttons.

Numbers n such that when n unit-diameter circles are arranged non-overlapping in the plane, and those circles are then enclosed in a rectangle, the area of the rectangle must be at least n