21876981 has 24 divisors (see below), whose sum is σ = 34730784. Its totient is φ = 12206880.

The previous prime is 21876973. The next prime is 21876983. The reversal of 21876981 is 18967812.

It is not a de Polignac number, because 21876981 - 2³ = 21876973 is a prime.

It is a super-2 number, since 2×21876981² = 957204595348722, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21876983) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4591 + ... + 8051.

It is an arithmetic number, because the mean of its divisors is an integer number (1447116).

Almost surely, 2^21876981 is an apocalyptic number.

21876981 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21876981 is a deficient number, since it is larger than the sum of its proper divisors (12853803).

21876981 is a wasteful number, since it uses less digits than its factorization.

21876981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3521 (or 3514 counting only the distinct ones).

The product of its digits is 48384, while the sum is 42.

The square root of 21876981 is about 4677.2835064811. The cubic root of 21876981 is about 279.6806776381.

The spelling of 21876981 in words is "twenty-one million, eight hundred seventy-six thousand, nine hundred eighty-one".