21308081 has 2 divisors, whose sum is σ = 21308082. Its totient is φ = 21308080.

The previous prime is 21308059. The next prime is 21308107. The reversal of 21308081 is 18080312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21307456 + 625 = 4616^2 + 25^2 .

It is a cyclic number.

It is not a de Polignac number, because 21308081 - 2⁶ = 21308017 is a prime.

It is a super-2 number, since 2×21308081² = 908068631805122, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21308681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10654040 + 10654041.

It is an arithmetic number, because the mean of its divisors is an integer number (10654041).

Almost surely, 2^21308081 is an apocalyptic number.

It is an amenable number.

21308081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21308081 is an equidigital number, since it uses as much as digits as its factorization.

21308081 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 384, while the sum is 23.

The square root of 21308081 is about 4616.0676988103. The cubic root of 21308081 is about 277.2350353462.

Adding to 21308081 its reverse (18080312), we get a palindrome (39388393).

It can be divided in two parts, 2 and 1308081, that multiplied together give a palindrome (2616162).

The spelling of 21308081 in words is "twenty-one million, three hundred eight thousand, eighty-one".