21661073647 has 4 divisors (see below), whose sum is σ = 21735002520. Its totient is φ = 21587144776.

The previous prime is 21661073627. The next prime is 21661073663. The reversal of 21661073647 is 74637016612.

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 21661073647 - 2³¹ = 19513589999 is a prime.

It is a super-2 number, since 2×21661073647² (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 (21661073627) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 36963997 + ... + 36964582.

It is an arithmetic number, because the mean of its divisors is an integer number (5433750630).

Almost surely, 2^21661073647 is an apocalyptic number.

21661073647 is a deficient number, since it is larger than the sum of its proper divisors (73928873).

21661073647 is an equidigital number, since it uses as much as digits as its factorization.

21661073647 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73928872.

The product of its (nonzero) digits is 254016, while the sum is 43.

The spelling of 21661073647 in words is "twenty-one billion, six hundred sixty-one million, seventy-three thousand, six hundred forty-seven".