21958609 has 2 divisors, whose sum is σ = 21958610. Its totient is φ = 21958608.

The previous prime is 21958591. The next prime is 21958631. The reversal of 21958609 is 90685912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21418384 + 540225 = 4628^2 + 735^2 .

It is a cyclic number.

It is not a de Polignac number, because 21958609 - 2¹⁷ = 21827537 is a prime.

It is not a weakly prime, because it can be changed into another prime (21958639) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10979304 + 10979305.

It is an arithmetic number, because the mean of its divisors is an integer number (10979305).

Almost surely, 2^21958609 is an apocalyptic number.

It is an amenable number.

21958609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21958609 is an equidigital number, since it uses as much as digits as its factorization.

21958609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 38880, while the sum is 40.

The square root of 21958609 is about 4686.0013871103. The cubic root of 21958609 is about 280.0280966703.

The spelling of 21958609 in words is "twenty-one million, nine hundred fifty-eight thousand, six hundred nine".