21509730 has 48 divisors (see below), whose sum is σ = 61012224. Its totient is φ = 5214240.

The previous prime is 21509723. The next prime is 21509731. The reversal of 21509730 is 3790512.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21509694 and 21509703.

It is not an unprimeable number, because it can be changed into a prime (21509731) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 9874 + ... + 11853.

It is an arithmetic number, because the mean of its divisors is an integer number (1271088).

Almost surely, 2^21509730 is an apocalyptic number.

21509730 is an abundant number, since it is smaller than the sum of its proper divisors (39502494).

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

21509730 is a wasteful number, since it uses less digits than its factorization.

21509730 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21751 (or 21748 counting only the distinct ones).

The product of its (nonzero) digits is 1890, while the sum is 27.

The square root of 21509730 is about 4637.8583419505. The cubic root of 21509730 is about 278.1068288427.

The spelling of 21509730 in words is "twenty-one million, five hundred nine thousand, seven hundred thirty".