21517380 has 48 divisors (see below), whose sum is σ = 66944640. Its totient is φ = 5737824.

The previous prime is 21517373. The next prime is 21517381. The reversal of 21517380 is 8371512.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21517381) 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, 19384 + ... + 20463.

It is an arithmetic number, because the mean of its divisors is an integer number (1394680).

Almost surely, 2^21517380 is an apocalyptic number.

21517380 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21517380 is an abundant number, since it is smaller than the sum of its proper divisors (45427260).

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

21517380 is a wasteful number, since it uses less digits than its factorization.

21517380 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39865 (or 39857 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 21517380 is about 4638.6830027498. The cubic root of 21517380 is about 278.1397947775.

Adding to 21517380 its reverse (8371512), we get a palindrome (29888892).

The spelling of 21517380 in words is "twenty-one million, five hundred seventeen thousand, three hundred eighty".