21638311 has 2 divisors, whose sum is σ = 21638312. Its totient is φ = 21638310.

The previous prime is 21638273. The next prime is 21638317. The reversal of 21638311 is 11383612.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21638311 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21638317) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10819155 + 10819156.

It is an arithmetic number, because the mean of its divisors is an integer number (10819156).

Almost surely, 2^21638311 is an apocalyptic number.

21638311 is a deficient number, since it is larger than the sum of its proper divisors (1).

21638311 is an equidigital number, since it uses as much as digits as its factorization.

21638311 is an evil number, because the sum of its binary digits is even.

The product of its digits is 864, while the sum is 25.

The square root of 21638311 is about 4651.6997968485. The cubic root of 21638311 is about 278.6598845356.

The spelling of 21638311 in words is "twenty-one million, six hundred thirty-eight thousand, three hundred eleven".