21653909 has 2 divisors, whose sum is σ = 21653910. Its totient is φ = 21653908.

The previous prime is 21653899. The next prime is 21653927. The reversal of 21653909 is 90935612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12229009 + 9424900 = 3497^2 + 3070^2 .

It is a cyclic number.

It is not a de Polignac number, because 21653909 - 2⁴ = 21653893 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is equal to p_1368674 and since 21653909 and 1368674 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21653959) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10826954 + 10826955.

It is an arithmetic number, because the mean of its divisors is an integer number (10826955).

Almost surely, 2^21653909 is an apocalyptic number.

It is an amenable number.

21653909 is a deficient number, since it is larger than the sum of its proper divisors (1).

21653909 is an equidigital number, since it uses as much as digits as its factorization.

21653909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 14580, while the sum is 35.

The square root of 21653909 is about 4653.3760862410. The cubic root of 21653909 is about 278.7268258802.

The spelling of 21653909 in words is "twenty-one million, six hundred fifty-three thousand, nine hundred nine".