21581442 has 24 divisors (see below), whose sum is σ = 47848944. Its totient is φ = 7026264.

The previous prime is 21581431. The next prime is 21581447. The reversal of 21581442 is 24418512.

21581442 is a `hidden beast` number, since 215 + 8 + 1 + 442 = 666.

It is not an unprimeable number, because it can be changed into a prime (21581447) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 13168 + ... + 14715.

It is an arithmetic number, because the mean of its divisors is an integer number (1993706).

Almost surely, 2^21581442 is an apocalyptic number.

21581442 is an abundant number, since it is smaller than the sum of its proper divisors (26267502).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21581442 is a wasteful number, since it uses less digits than its factorization.

21581442 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27934 (or 27931 counting only the distinct ones).

The product of its digits is 2560, while the sum is 27.

The square root of 21581442 is about 4645.5830635131. The cubic root of 21581442 is about 278.4155491959.

Adding to 21581442 its reverse (24418512), we get a palindrome (45999954).

It can be divided in two parts, 2158 and 1442, that added together give a square (3600 = 60²).

The spelling of 21581442 in words is "twenty-one million, five hundred eighty-one thousand, four hundred forty-two".