21501921 has 16 divisors (see below), whose sum is σ = 33651584. Its totient is φ = 11954304.

The previous prime is 21501913. The next prime is 21501929. The reversal of 21501921 is 12910512.

It is an interprime number because it is at equal distance from previous prime (21501913) and next prime (21501929).

It is not a de Polignac number, because 21501921 - 2³ = 21501913 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21501929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13060 + ... + 14613.

It is an arithmetic number, because the mean of its divisors is an integer number (2103224).

Almost surely, 2^21501921 is an apocalyptic number.

21501921 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21501921 is a deficient number, since it is larger than the sum of its proper divisors (12149663).

21501921 is a wasteful number, since it uses less digits than its factorization.

21501921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27720.

The product of its (nonzero) digits is 180, while the sum is 21.

The square root of 21501921 is about 4637.0163898783. The cubic root of 21501921 is about 278.0731696709.

It can be divided in two parts, 21501 and 921, that added together give a palindrome (22422).

The spelling of 21501921 in words is "twenty-one million, five hundred one thousand, nine hundred twenty-one".