21420581 has 24 divisors (see below), whose sum is σ = 27933120. Its totient is φ = 16039296.

The previous prime is 21420569. The next prime is 21420587. The reversal of 21420581 is 18502412.

It is not a de Polignac number, because 21420581 - 2¹⁰ = 21419557 is a prime.

It is a super-2 number, since 2×21420581² = 917682580755122, which contains 22 as substring.

It is a Duffinian number.

It is a zygodrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21420587) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 22001 + ... + 22953.

It is an arithmetic number, because the mean of its divisors is an integer number (1163880).

Almost surely, 2^21420581 is an apocalyptic number.

It is an amenable number.

21420581 is a deficient number, since it is larger than the sum of its proper divisors (6512539).

21420581 is a wasteful number, since it uses less digits than its factorization.

21420581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1005 (or 992 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 23.

The square root of 21420581 is about 4628.2373534641. The cubic root of 21420581 is about 277.7220839394.

Adding to 21420581 its reverse (18502412), we get a palindrome (39922993).

The spelling of 21420581 in words is "twenty-one million, four hundred twenty thousand, five hundred eighty-one".