21431657 has 4 divisors (see below), whose sum is σ = 23080260. Its totient is φ = 19783056.

The previous prime is 21431647. The next prime is 21431681. The reversal of 21431657 is 75613412.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14055001 + 7376656 = 3749^2 + 2716^2 .

It is a cyclic number.

It is not a de Polignac number, because 21431657 - 2⁶ = 21431593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21431647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 824282 + ... + 824307.

It is an arithmetic number, because the mean of its divisors is an integer number (5770065).

Almost surely, 2^21431657 is an apocalyptic number.

It is an amenable number.

21431657 is a deficient number, since it is larger than the sum of its proper divisors (1648603).

21431657 is a wasteful number, since it uses less digits than its factorization.

21431657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1648602.

The product of its digits is 5040, while the sum is 29.

The square root of 21431657 is about 4629.4337666717. The cubic root of 21431657 is about 277.7699432042.

The spelling of 21431657 in words is "twenty-one million, four hundred thirty-one thousand, six hundred fifty-seven".