21123291 has 16 divisors (see below), whose sum is σ = 32670464. Its totient is φ = 11889504.

The previous prime is 21123287. The next prime is 21123293. The reversal of 21123291 is 19232112.

It is not a de Polignac number, because 21123291 - 2² = 21123287 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 not an unprimeable number, because it can be changed into a prime (21123293) 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, 6100 + ... + 8913.

It is an arithmetic number, because the mean of its divisors is an integer number (2041904).

Almost surely, 2^21123291 is an apocalyptic number.

21123291 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21123291 is a deficient number, since it is larger than the sum of its proper divisors (11547173).

21123291 is a wasteful number, since it uses less digits than its factorization.

21123291 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15090.

The product of its digits is 216, while the sum is 21.

The square root of 21123291 is about 4596.0081592617. The cubic root of 21123291 is about 276.4312859061.

The spelling of 21123291 in words is "twenty-one million, one hundred twenty-three thousand, two hundred ninety-one".