21895409 has 2 divisors, whose sum is σ = 21895410. Its totient is φ = 21895408.

The previous prime is 21895397. The next prime is 21895411. The reversal of 21895409 is 90459812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11751184 + 10144225 = 3428^2 + 3185^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21895409 is a prime.

Together with 21895411, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21895469) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10947704 + 10947705.

It is an arithmetic number, because the mean of its divisors is an integer number (10947705).

Almost surely, 2^21895409 is an apocalyptic number.

It is an amenable number.

21895409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21895409 is an equidigital number, since it uses as much as digits as its factorization.

21895409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 25920, while the sum is 38.

The square root of 21895409 is about 4679.2530386804. The cubic root of 21895409 is about 279.7591849523.

The spelling of 21895409 in words is "twenty-one million, eight hundred ninety-five thousand, four hundred nine".