81690788 has 6 divisors (see below), whose sum is σ = 142958886. Its totient is φ = 40845392.

The previous prime is 81690787. The next prime is 81690793. The reversal of 81690788 is 88709618.

It can be written as a sum of positive squares in only one way, i.e., 56670784 + 25020004 = 7528^2 + 5002^2 .

It is not an unprimeable number, because it can be changed into a prime (81690787) 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 as a sum of consecutive naturals, namely, 10211345 + ... + 10211352.

It is an arithmetic number, because the mean of its divisors is an integer number (23826481).

Almost surely, 2^81690788 is an apocalyptic number.

It is an amenable number.

81690788 is a deficient number, since it is larger than the sum of its proper divisors (61268098).

81690788 is a wasteful number, since it uses less digits than its factorization.

81690788 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20422701 (or 20422699 counting only the distinct ones).

The product of its (nonzero) digits is 193536, while the sum is 47.

The square root of 81690788 is about 9038.2956357933. The cubic root of 81690788 is about 433.9013770680.

The spelling of 81690788 in words is "eighty-one million, six hundred ninety thousand, seven hundred eighty-eight".