21685735957 has 4 divisors (see below), whose sum is σ = 21900446316. Its totient is φ = 21471025600.

The previous prime is 21685735943. The next prime is 21685735979. The reversal of 21685735957 is 75953758612.

It is a happy number.

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 20495071921 + 1190664036 = 143161^2 + 34506^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21685735957 is a prime.

It is a super-2 number, since 2×21685735957² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685745957) 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, 107355028 + ... + 107355229.

It is an arithmetic number, because the mean of its divisors is an integer number (5475111579).

Almost surely, 2^21685735957 is an apocalyptic number.

It is an amenable number.

21685735957 is a deficient number, since it is larger than the sum of its proper divisors (214710359).

21685735957 is a wasteful number, since it uses less digits than its factorization.

21685735957 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 214710358.

The product of its digits is 15876000, while the sum is 58.

The spelling of 21685735957 in words is "twenty-one billion, six hundred eighty-five million, seven hundred thirty-five thousand, nine hundred fifty-seven".