200

2 + 0 + 0

Digit sum repeated until one digit remains; equals n mod 9 (with 9 for multiples of 9).

Reverses to 2.

Divisible by 2.

Composite — it factors as 2^3 × 5^2.

2 distinct prime factors, 5 with multiplicity.

At least one prime appears squared.

Every prime factor appears at least squared.

Zero, because a squared prime divides n.

A gap of 12 between them.

1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 200

The proper divisors — everything except n itself.

Its proper divisors overshoot by 65.

How many integers from 1 to n share no factor with n.

2² + 14² = 200 · 10² + 10² = 200

Legendre's three-square theorem allows it.

Lagrange's four-square theorem: every non-negative integer is, without exception.

The smallest pair of primes summing to n. Goldbach’s conjecture says one always exists; it remains unproven.

Not triangular, square, pentagonal, hexagonal, cubic, Fibonacci, Lucas, Catalan, factorial or a power of two.

Summing the squares of its digits falls into the 4 → 16 → 37 → … → 4 cycle.

Divisible by its digit sum 2 — 200 ÷ 2 = 100.

Peaks at 200 along the way.