21008501 has 2 divisors, whose sum is σ = 21008502. Its totient is φ = 21008500.

The previous prime is 21008497. The next prime is 21008503. The reversal of 21008501 is 10580012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20921476 + 87025 = 4574^2 + 295^2 .

It is a cyclic number.

It is not a de Polignac number, because 21008501 - 2² = 21008497 is a prime.

It is a super-2 number, since 2×21008501² = 882714228534002, which contains 22 as substring.

Together with 21008503, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21008501.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21008503) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10504250 + 10504251.

It is an arithmetic number, because the mean of its divisors is an integer number (10504251).

Almost surely, 2^21008501 is an apocalyptic number.

It is an amenable number.

21008501 is a deficient number, since it is larger than the sum of its proper divisors (1).

21008501 is an equidigital number, since it uses as much as digits as its factorization.

21008501 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 80, while the sum is 17.

The square root of 21008501 is about 4583.5031362485. The cubic root of 21008501 is about 275.9296405752.

Adding to 21008501 its reverse (10580012), we get a palindrome (31588513).

It can be divided in two parts, 2100 and 8501, that added together give a palindrome (10601).

The spelling of 21008501 in words is "twenty-one million, eight thousand, five hundred one".