21891261 has 12 divisors (see below), whose sum is σ = 33390816. Its totient is φ = 12497040.

The previous prime is 21891227. The next prime is 21891269. The reversal of 21891261 is 16219812.

It is a happy number.

It is not a de Polignac number, because 21891261 - 2¹⁹ = 21366973 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21891269) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 20931 + ... + 21951.

It is an arithmetic number, because the mean of its divisors is an integer number (2782568).

Almost surely, 2^21891261 is an apocalyptic number.

21891261 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21891261 is a deficient number, since it is larger than the sum of its proper divisors (11499555).

21891261 is an frugal number, since it uses more digits than its factorization.

21891261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2052 (or 1031 counting only the distinct ones).

The product of its digits is 1728, while the sum is 30.

The square root of 21891261 is about 4678.8097845499. The cubic root of 21891261 is about 279.7415174071.

The spelling of 21891261 in words is "twenty-one million, eight hundred ninety-one thousand, two hundred sixty-one".