21216981 has 8 divisors (see below), whose sum is σ = 28348000. Its totient is φ = 14115312.

The previous prime is 21216961. The next prime is 21216983. The reversal of 21216981 is 18961212.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21216981 - 2⁹ = 21216469 is a prime.

It is a super-2 number, since 2×21216981² = 900320565508722, which contains 22 as substring.

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

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216983) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5590 + ... + 8583.

It is an arithmetic number, because the mean of its divisors is an integer number (3543500).

Almost surely, 2^21216981 is an apocalyptic number.

It is an amenable number.

21216981 is a deficient number, since it is larger than the sum of its proper divisors (7131019).

21216981 is a wasteful number, since it uses less digits than its factorization.

21216981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14675.

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

The square root of 21216981 is about 4606.1894229395. The cubic root of 21216981 is about 276.8393765262.

The spelling of 21216981 in words is "twenty-one million, two hundred sixteen thousand, nine hundred eighty-one".