21312081 has 12 divisors (see below), whose sum is σ = 35181952. Its totient is φ = 12178296.

The previous prime is 21312079. The next prime is 21312107. The reversal of 21312081 is 18021312.

It is not a de Polignac number, because 21312081 - 2¹ = 21312079 is a prime.

It is a super-2 number, since 2×21312081² = 908409593101122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21312001) 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, 169081 + ... + 169206.

Almost surely, 2^21312081 is an apocalyptic number.

21312081 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21312081 is a deficient number, since it is larger than the sum of its proper divisors (13869871).

21312081 is a wasteful number, since it uses less digits than its factorization.

21312081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 338300 (or 338297 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 18.

The square root of 21312081 is about 4616.5009476875. The cubic root of 21312081 is about 277.2523819851.

Adding to 21312081 its reverse (18021312), we get a palindrome (39333393).

The spelling of 21312081 in words is "twenty-one million, three hundred twelve thousand, eighty-one".