21663457 has 8 divisors (see below), whose sum is σ = 23497992. Its totient is φ = 19891200.

The previous prime is 21663437. The next prime is 21663497. The reversal of 21663457 is 75436612.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 512656 + 21150801 = 716^2 + 4599^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21663457 - 2⁷ = 21663329 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21663427) 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, 14844 + ... + 16237.

It is an arithmetic number, because the mean of its divisors is an integer number (2937249).

Almost surely, 2^21663457 is an apocalyptic number.

It is an amenable number.

21663457 is a deficient number, since it is larger than the sum of its proper divisors (1834535).

21663457 is a wasteful number, since it uses less digits than its factorization.

21663457 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31139.

The product of its digits is 30240, while the sum is 34.

The square root of 21663457 is about 4654.4018949807. The cubic root of 21663457 is about 278.7677868090.

The spelling of 21663457 in words is "twenty-one million, six hundred sixty-three thousand, four hundred fifty-seven".