21123420 has 24 divisors (see below), whose sum is σ = 59145744. Its totient is φ = 5632896.

The previous prime is 21123391. The next prime is 21123457. The reversal of 21123420 is 2432112.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21123420.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 175969 + ... + 176088.

It is an arithmetic number, because the mean of its divisors is an integer number (2464406).

Almost surely, 2^21123420 is an apocalyptic number.

21123420 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21123420 is an abundant number, since it is smaller than the sum of its proper divisors (38022324).

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

21123420 is a wasteful number, since it uses less digits than its factorization.

21123420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 352069 (or 352067 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 15.

The square root of 21123420 is about 4596.0221931579. The cubic root of 21123420 is about 276.4318486271.

Adding to 21123420 its reverse (2432112), we get a palindrome (23555532).

The spelling of 21123420 in words is "twenty-one million, one hundred twenty-three thousand, four hundred twenty".