21643747957 has 16 divisors (see below), whose sum is σ = 23950935792. Its totient is φ = 19428871680.

The previous prime is 21643747949. The next prime is 21643747969. The reversal of 21643747957 is 75974734612.

It can be written as a sum of positive squares in 8 ways, for example, as 81468676 + 21562279281 = 9026^2 + 146841^2 .

It is not a de Polignac number, because 21643747957 - 2³ = 21643747949 is a prime.

It is a super-2 number, since 2×21643747957² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21643747898 and 21643747907.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21643747987) 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, 1019313 + ... + 1040329.

It is an arithmetic number, because the mean of its divisors is an integer number (1496933487).

Almost surely, 2^21643747957 is an apocalyptic number.

It is an amenable number.

21643747957 is a deficient number, since it is larger than the sum of its proper divisors (2307187835).

21643747957 is a wasteful number, since it uses less digits than its factorization.

21643747957 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23208.

The product of its digits is 8890560, while the sum is 55.

The spelling of 21643747957 in words is "twenty-one billion, six hundred forty-three million, seven hundred forty-seven thousand, nine hundred fifty-seven".