99971821 has 8 divisors (see below), whose sum is σ = 101514680. Its totient is φ = 98433792.

The previous prime is 99971813. The next prime is 99971827. The reversal of 99971821 is 12817999.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 1188100 + 98783721 = 1090^2 + 9939^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a 4-Lehmer number, since φ(99971821) divides (99971821-1)⁴.

It is a cyclic number.

It is not a de Polignac number, because 99971821 - 2³ = 99971813 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 (99971827) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 81811 + ... + 83023.

It is an arithmetic number, because the mean of its divisors is an integer number (12689335).

It is a Poulet number, since it divides 2^99971820-1.

Almost surely, 2^99971821 is an apocalyptic number.

It is an amenable number.

99971821 is a deficient number, since it is larger than the sum of its proper divisors (1542859).

99971821 is a wasteful number, since it uses less digits than its factorization.

99971821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2415.

The product of its digits is 81648, while the sum is 46.

The square root of 99971821 is about 9998.5909507290. The cubic root of 99971821 is about 464.1152808215.

The spelling of 99971821 in words is "ninety-nine million, nine hundred seventy-one thousand, eight hundred twenty-one".