15 is:
a triangular number.
a hexagonal number.
a pentatope number.
the 5th Bell number (i.e. the number of partitions for a set of size 4).
a composite number ; its proper divisors being 1, 3 and 5.
the number of supersingular primes.
a repdigit in binary (1111) and quaternary (33).
Challenge: This puzzle has not yet been solved in {size} size. Be the first to complete it.
