21942921 has 32 divisors (see below), whose sum is σ = 39287808. Its totient is φ = 10520640.

The previous prime is 21942919. The next prime is 21942923. The reversal of 21942921 is 12924912.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21942919) and next prime (21942923).

It is not a de Polignac number, because 21942921 - 2¹ = 21942919 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21942923) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 651 + ... + 6656.

It is an arithmetic number, because the mean of its divisors is an integer number (1227744).

Almost surely, 2^21942921 is an apocalyptic number.

21942921 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21942921 is a deficient number, since it is larger than the sum of its proper divisors (17344887).

21942921 is a wasteful number, since it uses less digits than its factorization.

21942921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7341.

The product of its digits is 2592, while the sum is 30.

The square root of 21942921 is about 4684.3271662001. The cubic root of 21942921 is about 279.9613934867.

Subtracting from 21942921 its reverse (12924912), we obtain a square (9018009 = 3003²).

It can be divided in two parts, 2194 and 2921, that added together give a palindrome (5115).

The spelling of 21942921 in words is "twenty-one million, nine hundred forty-two thousand, nine hundred twenty-one".