81669021 has 32 divisors (see below), whose sum is σ = 130498560. Its totient is φ = 44419584.

The previous prime is 81668971. The next prime is 81669023. The reversal of 81669021 is 12096618.

It is not a de Polignac number, because 81669021 - 2⁷ = 81668893 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81669023) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 170260 + ... + 170738.

It is an arithmetic number, because the mean of its divisors is an integer number (4078080).

Almost surely, 2^81669021 is an apocalyptic number.

It is an amenable number.

81669021 is a deficient number, since it is larger than the sum of its proper divisors (48829539).

81669021 is a wasteful number, since it uses less digits than its factorization.

81669021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 865.

The product of its (nonzero) digits is 5184, while the sum is 33.

The square root of 81669021 is about 9037.0914015517. The cubic root of 81669021 is about 433.8628351039.

The spelling of 81669021 in words is "eighty-one million, six hundred sixty-nine thousand, twenty-one".