21613997 has 4 divisors (see below), whose sum is σ = 22553760. Its totient is φ = 20674236.

The previous prime is 21613981. The next prime is 21614017. The reversal of 21613997 is 79931612.

It is a happy number.

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 21613997 - 2⁴ = 21613981 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21613997.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21613897) 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, 469847 + ... + 469892.

It is an arithmetic number, because the mean of its divisors is an integer number (5638440).

Almost surely, 2^21613997 is an apocalyptic number.

It is an amenable number.

21613997 is a deficient number, since it is larger than the sum of its proper divisors (939763).

21613997 is an equidigital number, since it uses as much as digits as its factorization.

21613997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 939762.

The product of its digits is 20412, while the sum is 38.

The square root of 21613997 is about 4649.0856090203. The cubic root of 21613997 is about 278.5554728784. Note that the first 3 decimals are identical.

The spelling of 21613997 in words is "twenty-one million, six hundred thirteen thousand, nine hundred ninety-seven".