21656497 has 4 divisors (see below), whose sum is σ = 21718900. Its totient is φ = 21594096.

The previous prime is 21656461. The next prime is 21656513. The reversal of 21656497 is 79465612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11771761 + 9884736 = 3431^2 + 3144^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21656497 is a prime.

It is a super-2 number, since 2×21656497² = 938007724622018, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21656597) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 30678 + ... + 31375.

It is an arithmetic number, because the mean of its divisors is an integer number (5429725).

Almost surely, 2^21656497 is an apocalyptic number.

It is an amenable number.

21656497 is a deficient number, since it is larger than the sum of its proper divisors (62403).

21656497 is an equidigital number, since it uses as much as digits as its factorization.

21656497 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62402.

The product of its digits is 90720, while the sum is 40.

The square root of 21656497 is about 4653.6541556072. The cubic root of 21656497 is about 278.7379295919.

The spelling of 21656497 in words is "twenty-one million, six hundred fifty-six thousand, four hundred ninety-seven".