21761891 has 2 divisors, whose sum is σ = 21761892. Its totient is φ = 21761890.

The previous prime is 21761881. The next prime is 21761899. The reversal of 21761891 is 19816712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21761891 - 2²² = 17567587 is a prime.

It is not a weakly prime, because it can be changed into another prime (21761899) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10880945 + 10880946.

It is an arithmetic number, because the mean of its divisors is an integer number (10880946).

Almost surely, 2^21761891 is an apocalyptic number.

21761891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21761891 is an equidigital number, since it uses as much as digits as its factorization.

21761891 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6048, while the sum is 35.

The square root of 21761891 is about 4664.9642013632. The cubic root of 21761891 is about 279.1893688327.

The spelling of 21761891 in words is "twenty-one million, seven hundred sixty-one thousand, eight hundred ninety-one".