21012981 has 24 divisors (see below), whose sum is σ = 31141152. Its totient is φ = 12592800.

The previous prime is 21012913. The next prime is 21012991. The reversal of 21012981 is 18921012.

It is not a de Polignac number, because 21012981 - 2¹⁰ = 21011957 is a prime.

It is a super-2 number, since 2×21012981² = 883090741012722, 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 (21012991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 38571 + ... + 39111.

It is an arithmetic number, because the mean of its divisors is an integer number (1297548).

Almost surely, 2^21012981 is an apocalyptic number.

It is an amenable number.

21012981 is a deficient number, since it is larger than the sum of its proper divisors (10128171).

21012981 is a wasteful number, since it uses less digits than its factorization.

21012981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 673 (or 662 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 24.

The square root of 21012981 is about 4583.9918193644. The cubic root of 21012981 is about 275.9492529047.

Adding to 21012981 its reverse (18921012), we get a palindrome (39933993).

The spelling of 21012981 in words is "twenty-one million, twelve thousand, nine hundred eighty-one".