21656289 has 4 divisors (see below), whose sum is σ = 28875056. Its totient is φ = 14437524.

The previous prime is 21656287. The next prime is 21656291. The reversal of 21656289 is 98265612.

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 an interprime number because it is at equal distance from previous prime (21656287) and next prime (21656291).

It is not a de Polignac number, because 21656289 - 2¹ = 21656287 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21656287) 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, 3609379 + ... + 3609384.

It is an arithmetic number, because the mean of its divisors is an integer number (7218764).

Almost surely, 2^21656289 is an apocalyptic number.

It is an amenable number.

21656289 is a deficient number, since it is larger than the sum of its proper divisors (7218767).

21656289 is an equidigital number, since it uses as much as digits as its factorization.

21656289 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7218766.

The product of its digits is 51840, while the sum is 39.

The square root of 21656289 is about 4653.6318075241. The cubic root of 21656289 is about 278.7370372088.

It can be divided in two parts, 21656 and 289, that added together give a triangular number (21945 = T₂₀₉).

The spelling of 21656289 in words is "twenty-one million, six hundred fifty-six thousand, two hundred eighty-nine".