21008997 has 8 divisors (see below), whose sum is σ = 31124480. Its totient is φ = 14005980.

The previous prime is 21008941. The next prime is 21009017. The reversal of 21008997 is 79980012.

It is a happy number.

It is not a de Polignac number, because 21008997 - 2¹² = 21004901 is a prime.

It is a Duffinian number.

It is a plaindrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21008497) 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, 389029 + ... + 389082.

It is an arithmetic number, because the mean of its divisors is an integer number (3890560).

Almost surely, 2^21008997 is an apocalyptic number.

21008997 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21008997 is a deficient number, since it is larger than the sum of its proper divisors (10115483).

21008997 is an equidigital number, since it uses as much as digits as its factorization.

21008997 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 778120 (or 778114 counting only the distinct ones).

The product of its (nonzero) digits is 9072, while the sum is 36.

The square root of 21008997 is about 4583.5572430155. The cubic root of 21008997 is about 275.9318120775.

The spelling of 21008997 in words is "twenty-one million, eight thousand, nine hundred ninety-seven".