21006457 has 4 divisors (see below), whose sum is σ = 22112080. Its totient is φ = 19900836.

The previous prime is 21006451. The next prime is 21006463. The reversal of 21006457 is 75460012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21006451) and next prime (21006463).

It is a cyclic number.

It is not a de Polignac number, because 21006457 - 2⁷ = 21006329 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21006451) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 552783 + ... + 552820.

It is an arithmetic number, because the mean of its divisors is an integer number (5528020).

Almost surely, 2^21006457 is an apocalyptic number.

It is an amenable number.

21006457 is a deficient number, since it is larger than the sum of its proper divisors (1105623).

21006457 is a wasteful number, since it uses less digits than its factorization.

21006457 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1105622.

The product of its (nonzero) digits is 1680, while the sum is 25.

The square root of 21006457 is about 4583.2801572673. The cubic root of 21006457 is about 275.9206915236.

Adding to 21006457 its reverse (75460012), we get a palindrome (96466469).

The spelling of 21006457 in words is "twenty-one million, six thousand, four hundred fifty-seven".