21509790 has 32 divisors (see below), whose sum is σ = 51752736. Its totient is φ = 5721600.

The previous prime is 21509783. The next prime is 21509797. The reversal of 21509790 is 9790512.

It is an interprime number because it is at equal distance from previous prime (21509783) and next prime (21509797).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21509797) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17434 + ... + 18626.

It is an arithmetic number, because the mean of its divisors is an integer number (1617273).

Almost surely, 2^21509790 is an apocalyptic number.

21509790 is an abundant number, since it is smaller than the sum of its proper divisors (30242946).

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

21509790 is a wasteful number, since it uses less digits than its factorization.

21509790 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1804.

The product of its (nonzero) digits is 5670, while the sum is 33.

The square root of 21509790 is about 4637.8648104489. The cubic root of 21509790 is about 278.1070874295.

The spelling of 21509790 in words is "twenty-one million, five hundred nine thousand, seven hundred ninety".