21007881 has 12 divisors (see below), whose sum is σ = 30711408. Its totient is φ = 13836024.

The previous prime is 21007879. The next prime is 21007891. The reversal of 21007881 is 18870012.

It is not a de Polignac number, because 21007881 - 2¹ = 21007879 is a prime.

It is a super-2 number, since 2×21007881² = 882662128220322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21007871) 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, 13315 + ... + 14808.

It is an arithmetic number, because the mean of its divisors is an integer number (2559284).

Almost surely, 2^21007881 is an apocalyptic number.

It is an amenable number.

21007881 is a deficient number, since it is larger than the sum of its proper divisors (9703527).

21007881 is a wasteful number, since it uses less digits than its factorization.

21007881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28212 (or 28209 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 27.

The square root of 21007881 is about 4583.4355018916. The cubic root of 21007881 is about 275.9269261493.

Adding to 21007881 its reverse (18870012), we get a palindrome (39877893).

The spelling of 21007881 in words is "twenty-one million, seven thousand, eight hundred eighty-one".