21008423 has 2 divisors, whose sum is σ = 21008424. Its totient is φ = 21008422.

The previous prime is 21008419. The next prime is 21008459. The reversal of 21008423 is 32480012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21008423 - 2² = 21008419 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21008395 and 21008404.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21008023) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10504211 + 10504212.

It is an arithmetic number, because the mean of its divisors is an integer number (10504212).

Almost surely, 2^21008423 is an apocalyptic number.

21008423 is a deficient number, since it is larger than the sum of its proper divisors (1).

21008423 is an equidigital number, since it uses as much as digits as its factorization.

21008423 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 20.

The square root of 21008423 is about 4583.4946274649. The cubic root of 21008423 is about 275.9292990859.

Adding to 21008423 its reverse (32480012), we get a palindrome (53488435).

The spelling of 21008423 in words is "twenty-one million, eight thousand, four hundred twenty-three".