21381611 has 2 divisors, whose sum is σ = 21381612. Its totient is φ = 21381610.

The previous prime is 21381557. The next prime is 21381617. The reversal of 21381611 is 11618312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21381611 - 2²² = 17187307 is a prime.

It is not a weakly prime, because it can be changed into another prime (21381617) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10690805 + 10690806.

It is an arithmetic number, because the mean of its divisors is an integer number (10690806).

Almost surely, 2^21381611 is an apocalyptic number.

21381611 is a deficient number, since it is larger than the sum of its proper divisors (1).

21381611 is an equidigital number, since it uses as much as digits as its factorization.

21381611 is an evil number, because the sum of its binary digits is even.

The product of its digits is 288, while the sum is 23.

The square root of 21381611 is about 4624.0254108298. The cubic root of 21381611 is about 277.5535637750.

Adding to 21381611 its reverse (11618312), we get a palindrome (32999923).

The spelling of 21381611 in words is "twenty-one million, three hundred eighty-one thousand, six hundred eleven".