21172866 has 32 divisors (see below), whose sum is σ = 49750848. Its totient is φ = 5922240.

The previous prime is 21172861. The next prime is 21172883. The reversal of 21172866 is 66827112.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is not an unprimeable number, because it can be changed into a prime (21172861) 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, 11481 + ... + 13196.

It is an arithmetic number, because the mean of its divisors is an integer number (1554714).

Almost surely, 2^21172866 is an apocalyptic number.

21172866 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

21172866 is an abundant number, since it is smaller than the sum of its proper divisors (28577982).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21172866 is a wasteful number, since it uses less digits than its factorization.

21172866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24706.

The product of its digits is 8064, while the sum is 33.

The square root of 21172866 is about 4601.3982657449. The cubic root of 21172866 is about 276.6473724065.

Adding to 21172866 its reverse (66827112), we get a palindrome (87999978).

The spelling of 21172866 in words is "twenty-one million, one hundred seventy-two thousand, eight hundred sixty-six".