21511881 has 12 divisors (see below), whose sum is σ = 32144580. Its totient is φ = 13846560.

The previous prime is 21511871. The next prime is 21511883. The reversal of 21511881 is 18811512.

It can be written as a sum of positive squares in 2 ways, for example, as 17139600 + 4372281 = 4140^2 + 2091^2 .

It is not a de Polignac number, because 21511881 - 2⁵ = 21511849 is a prime.

It is a super-2 number, since 2×21511881² = 925522048316322, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21511883) 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, 40950 + ... + 41471.

It is an arithmetic number, because the mean of its divisors is an integer number (2678715).

Almost surely, 2^21511881 is an apocalyptic number.

It is an amenable number.

21511881 is a deficient number, since it is larger than the sum of its proper divisors (10632699).

21511881 is a wasteful number, since it uses less digits than its factorization.

21511881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82456 (or 82453 counting only the distinct ones).

The product of its digits is 640, while the sum is 27.

The square root of 21511881 is about 4638.0902319813. The cubic root of 21511881 is about 278.1160988777.

The spelling of 21511881 in words is "twenty-one million, five hundred eleven thousand, eight hundred eighty-one".