90999821 has 4 divisors (see below), whose sum is σ = 99272544. Its totient is φ = 82727100.

The previous prime is 90999817. The next prime is 90999851. The reversal of 90999821 is 12899909.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 90999821 - 2² = 90999817 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (90999851) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4136345 + ... + 4136366.

It is an arithmetic number, because the mean of its divisors is an integer number (24818136).

Almost surely, 2^90999821 is an apocalyptic number.

It is an amenable number.

90999821 is a deficient number, since it is larger than the sum of its proper divisors (8272723).

90999821 is a wasteful number, since it uses less digits than its factorization.

90999821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8272722.

The product of its (nonzero) digits is 104976, while the sum is 47.

The square root of 90999821 is about 9539.3826320156. The cubic root of 90999821 is about 449.7938496074.

It can be divided in two parts, 909998 and 21, that added together give a palindrome (910019).

The spelling of 90999821 in words is "ninety million, nine hundred ninety-nine thousand, eight hundred twenty-one".