21777641 has 2 divisors, whose sum is σ = 21777642. Its totient is φ = 21777640.

The previous prime is 21777631. The next prime is 21777643. The reversal of 21777641 is 14677712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20894041 + 883600 = 4571^2 + 940^2 .

It is a cyclic number.

It is not a de Polignac number, because 21777641 - 2⁶ = 21777577 is a prime.

It is a Sophie Germain prime.

Together with 21777643, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21777643) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10888820 + 10888821.

It is an arithmetic number, because the mean of its divisors is an integer number (10888821).

Almost surely, 2^21777641 is an apocalyptic number.

It is an amenable number.

21777641 is a deficient number, since it is larger than the sum of its proper divisors (1).

21777641 is an equidigital number, since it uses as much as digits as its factorization.

21777641 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16464, while the sum is 35.

The square root of 21777641 is about 4666.6520118818. The cubic root of 21777641 is about 279.2567063045.

The spelling of 21777641 in words is "twenty-one million, seven hundred seventy-seven thousand, six hundred forty-one".