81000021 has 16 divisors (see below), whose sum is σ = 113883840. Its totient is φ = 51068160.

The previous prime is 81000013. The next prime is 81000037. The reversal of 81000021 is 12000018.

It is a happy number.

It is not a de Polignac number, because 81000021 - 2³ = 81000013 is a prime.

It is a super-2 number, since 2×81000021² = 13122006804000882, which contains 22 as substring.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 80999970 and 81000006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81000001) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 49411 + ... + 51023.

It is an arithmetic number, because the mean of its divisors is an integer number (7117740).

Almost surely, 2^81000021 is an apocalyptic number.

It is an amenable number.

81000021 is a deficient number, since it is larger than the sum of its proper divisors (32883819).

81000021 is a wasteful number, since it uses less digits than its factorization.

81000021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2516.

The product of its (nonzero) digits is 16, while the sum is 12.

The square root of 81000021 is about 9000.0011666666. The cubic root of 81000021 is about 432.6749084839.

Adding to 81000021 its reverse (12000018), we get a palindrome (93000039).

The spelling of 81000021 in words is "eighty-one million, twenty-one", and thus it is an aban number and an uban number.