21581137 has 2 divisors, whose sum is σ = 21581138. Its totient is φ = 21581136.

The previous prime is 21581111. The next prime is 21581167. The reversal of 21581137 is 73118512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21150801 + 430336 = 4599^2 + 656^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21581137 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21581167) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10790568 + 10790569.

It is an arithmetic number, because the mean of its divisors is an integer number (10790569).

Almost surely, 2^21581137 is an apocalyptic number.

It is an amenable number.

21581137 is a deficient number, since it is larger than the sum of its proper divisors (1).

21581137 is an equidigital number, since it uses as much as digits as its factorization.

21581137 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1680, while the sum is 28.

The square root of 21581137 is about 4645.5502365167. The cubic root of 21581137 is about 278.4142376193.

Adding to 21581137 its reverse (73118512), we get a palindrome (94699649).

The spelling of 21581137 in words is "twenty-one million, five hundred eighty-one thousand, one hundred thirty-seven".