21315657 has 16 divisors (see below), whose sum is σ = 31515840. Its totient is φ = 12705600.

The previous prime is 21315649. The next prime is 21315661. The reversal of 21315657 is 75651312.

It is not a de Polignac number, because 21315657 - 2³ = 21315649 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21315607) 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, 3282 + ... + 7307.

It is an arithmetic number, because the mean of its divisors is an integer number (1969740).

Almost surely, 2^21315657 is an apocalyptic number.

It is an amenable number.

21315657 is a deficient number, since it is larger than the sum of its proper divisors (10200183).

21315657 is a wasteful number, since it uses less digits than its factorization.

21315657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10664.

The product of its digits is 6300, while the sum is 30.

The square root of 21315657 is about 4616.8882377636. Note that the first 3 decimals coincide. The cubic root of 21315657 is about 277.2678880427.

Adding to 21315657 its reverse (75651312), we get a palindrome (96966969).

The spelling of 21315657 in words is "twenty-one million, three hundred fifteen thousand, six hundred fifty-seven".