21517137 has 8 divisors (see below), whose sum is σ = 31877280. Its totient is φ = 14344740.

The previous prime is 21517127. The next prime is 21517163. The reversal of 21517137 is 73171512.

It is a happy number.

It is not a de Polignac number, because 21517137 - 2⁶ = 21517073 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 796931 = 21517137 / (2 + 1 + 5 + 1 + 7 + 1 + 3 + 7).

It is a self number, because there is not a number n which added to its sum of digits gives 21517137.

It is not an unprimeable number, because it can be changed into a prime (21517127) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 398439 + ... + 398492.

It is an arithmetic number, because the mean of its divisors is an integer number (3984660).

Almost surely, 2^21517137 is an apocalyptic number.

21517137 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21517137 is a deficient number, since it is larger than the sum of its proper divisors (10360143).

21517137 is an equidigital number, since it uses as much as digits as its factorization.

21517137 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 796940 (or 796934 counting only the distinct ones).

The product of its digits is 1470, while the sum is 27.

The square root of 21517137 is about 4638.6568098966. The cubic root of 21517137 is about 278.1387477445.

Adding to 21517137 its reverse (73171512), we get a palindrome (94688649).

The spelling of 21517137 in words is "twenty-one million, five hundred seventeen thousand, one hundred thirty-seven".