21515970 has 64 divisors (see below), whose sum is σ = 61067520. Its totient is φ = 4747008.

The previous prime is 21515957. The next prime is 21515983. The reversal of 21515970 is 7951512.

It is an interprime number because it is at equal distance from previous prime (21515957) and next prime (21515983).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4324 + ... + 7856.

It is an arithmetic number, because the mean of its divisors is an integer number (954180).

Almost surely, 2^21515970 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21515970, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30533760).

21515970 is an abundant number, since it is smaller than the sum of its proper divisors (39551550).

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

21515970 is a wasteful number, since it uses less digits than its factorization.

21515970 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3579.

The product of its (nonzero) digits is 3150, while the sum is 30.

The square root of 21515970 is about 4638.5310174666. The cubic root of 21515970 is about 278.1337192907.

The spelling of 21515970 in words is "twenty-one million, five hundred fifteen thousand, nine hundred seventy".