mscroggs.co.uk

mscroggs.co.uk

blog puzzles academic talks contact subscribe ↓ ☰ ↓

Advent calendar 2025

21 December

This puzzle was part of the 2025 Advent calendar.

All 2025 advent puzzles ~ More information

There are ten ways to make a list of four As and Bs that don't contain an even* number of consecutive As:

B,B,B,B
A,B,B,B
B,A,B,B
B,B,A,B
B,B,B,A

A,B,A,B
A,B,B,A
B,A,B,A
A,A,A,B
B,A,A,A

How many ways are there to make a list of eleven As and Bs that don't contain an even number of consecutive As?

* We don't count 0 consecutive As as being an even number of consecutive As.

Show answer

Tags: lists, sets, even numbers

Archive

Show me a random puzzle

Most recent collections

Advent calendar 2025

Advent calendar 2024

Advent calendar 2023

Advent calendar 2022

List of all puzzles

Tags

ellipses volume the only crossnumber spheres factors axes chalkdust crossnumber parabolas scales pascal's triangle powers triangles addition cards geometric means games decahedra quadrilaterals planes routes palindromes ave multiples square roots functions probabilty even numbers averages cryptic clues regular shapes partitions irreducible numbers tangents tiling algebra lines logic shape star numbers rugby consecutive numbers books combinatorics shapes neighbours factorials square numbers menace products polygons prime numbers squares complex numbers dodecagons differentiation calculus digital clocks cryptic crossnumbers christmas taxicab geometry number median chess multiplication quadratics digital products sequences colouring remainders symmetry digits gerrymandering integers crosswords geometric mean hexagons means crossnumbers bases consecutive integers advent binary doubling clocks cubics range albgebra floors xor perfect numbers speed fractions coins arrows odd numbers 3d shapes percentages polynomials medians sets multiplaction squares mean grids people maths expansions elections pentagons geometry 2d shapes numbers angles balancing perimeter wordplay integration division probability circles graphs chocolate sums time lists surds tournaments rectangles dice trigonometry sum to infinity dates dominos folding tube maps cube numbers area coordinates unit fractions sport prime factors triangle numbers money indices determinants matrices proportion square grids

Archive

Show me a random puzzle
▼ show ▼

© Matthew Scroggs 2012–2026