21637449947 has 4 divisors (see below), whose sum is σ = 21638787216. Its totient is φ = 21636112680.

The previous prime is 21637449943. The next prime is 21637449961. The reversal of 21637449947 is 74994473612.

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

It is a cyclic number.

It is not a de Polignac number, because 21637449947 - 2² = 21637449943 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21637449892 and 21637449901.

It is not an unprimeable number, because it can be changed into a prime (21637449943) 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, 644063 + ... + 676824.

It is an arithmetic number, because the mean of its divisors is an integer number (5409696804).

Almost surely, 2^21637449947 is an apocalyptic number.

21637449947 is a deficient number, since it is larger than the sum of its proper divisors (1337269).

21637449947 is a wasteful number, since it uses less digits than its factorization.

21637449947 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1337268.

The product of its digits is 9144576, while the sum is 56.

The spelling of 21637449947 in words is "twenty-one billion, six hundred thirty-seven million, four hundred forty-nine thousand, nine hundred forty-seven".