21010581 has 6 divisors (see below), whose sum is σ = 30348630. Its totient is φ = 14007048.

The previous prime is 21010579. The next prime is 21010601. The reversal of 21010581 is 18501012.

It can be written as a sum of positive squares in only one way, i.e., 15563025 + 5447556 = 3945^2 + 2334^2 .

It is not a de Polignac number, because 21010581 - 2¹ = 21010579 is a prime.

It is a super-2 number, since 2×21010581² = 882889027915122, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21010501) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1167246 + ... + 1167263.

It is an arithmetic number, because the mean of its divisors is an integer number (5058105).

Almost surely, 2^21010581 is an apocalyptic number.

It is an amenable number.

21010581 is a deficient number, since it is larger than the sum of its proper divisors (9338049).

21010581 is a wasteful number, since it uses less digits than its factorization.

21010581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2334515 (or 2334512 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 18.

The square root of 21010581 is about 4583.7300313173. The cubic root of 21010581 is about 275.9387466463.

Adding to 21010581 its reverse (18501012), we get a palindrome (39511593).

The spelling of 21010581 in words is "twenty-one million, ten thousand, five hundred eighty-one".