21006523 has 2 divisors, whose sum is σ = 21006524. Its totient is φ = 21006522.

The previous prime is 21006511. The next prime is 21006547. The reversal of 21006523 is 32560012.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21006523 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21006523.

It is not a weakly prime, because it can be changed into another prime (21006563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10503261 + 10503262.

It is an arithmetic number, because the mean of its divisors is an integer number (10503262).

Almost surely, 2^21006523 is an apocalyptic number.

21006523 is a deficient number, since it is larger than the sum of its proper divisors (1).

21006523 is an equidigital number, since it uses as much as digits as its factorization.

21006523 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 360, while the sum is 19.

The square root of 21006523 is about 4583.2873573452. The cubic root of 21006523 is about 275.9209804943.

Adding to 21006523 its reverse (32560012), we get a palindrome (53566535).

The spelling of 21006523 in words is "twenty-one million, six thousand, five hundred twenty-three".