21661147 has 8 divisors (see below), whose sum is σ = 22649760. Its totient is φ = 20676480.

The previous prime is 21661141. The next prime is 21661151. The reversal of 21661147 is 74116612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21661147 - 2¹⁵ = 21628379 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21661141) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19729 + ... + 20797.

It is an arithmetic number, because the mean of its divisors is an integer number (2831220).

Almost surely, 2^21661147 is an apocalyptic number.

21661147 is a deficient number, since it is larger than the sum of its proper divisors (988613).

21661147 is a wasteful number, since it uses less digits than its factorization.

21661147 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1973.

The product of its digits is 2016, while the sum is 28.

The square root of 21661147 is about 4654.1537361802. The cubic root of 21661147 is about 278.7578780107.

Adding to 21661147 its reverse (74116612), we get a palindrome (95777759).

The spelling of 21661147 in words is "twenty-one million, six hundred sixty-one thousand, one hundred forty-seven".