21521730 has 32 divisors (see below), whose sum is σ = 51899904. Its totient is φ = 5711616.

The previous prime is 21521701. The next prime is 21521743. The reversal of 21521730 is 3712512.

It is a zygodrome in base 9.

It is a junction number, because it is equal to n+sod(n) for n = 21521697 and 21521706.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5082 + ... + 8298.

It is an arithmetic number, because the mean of its divisors is an integer number (1621872).

Almost surely, 2^21521730 is an apocalyptic number.

21521730 is an abundant number, since it is smaller than the sum of its proper divisors (30378174).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21521730 is a wasteful number, since it uses less digits than its factorization.

21521730 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3450.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21521730 is about 4639.1518621403. The cubic root of 21521730 is about 278.1585366284.

It can be divided in two parts, 215 and 21730, that added together give a triangular number (21945 = T₂₀₉).

The spelling of 21521730 in words is "twenty-one million, five hundred twenty-one thousand, seven hundred thirty".