21517021 has 2 divisors, whose sum is σ = 21517022. Its totient is φ = 21517020.

The previous prime is 21516961. The next prime is 21517031. The reversal of 21517021 is 12071512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16088121 + 5428900 = 4011^2 + 2330^2 .

It is a cyclic number.

It is not a de Polignac number, because 21517021 - 2⁷ = 21516893 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21517021.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21517031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10758510 + 10758511.

It is an arithmetic number, because the mean of its divisors is an integer number (10758511).

Almost surely, 2^21517021 is an apocalyptic number.

It is an amenable number.

21517021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21517021 is an equidigital number, since it uses as much as digits as its factorization.

21517021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 140, while the sum is 19.

The square root of 21517021 is about 4638.6443062602. The cubic root of 21517021 is about 278.1382479234.

Adding to 21517021 its reverse (12071512), we get a palindrome (33588533).

The spelling of 21517021 in words is "twenty-one million, five hundred seventeen thousand, twenty-one".