21957779 has 2 divisors, whose sum is σ = 21957780. Its totient is φ = 21957778.

The previous prime is 21957763. The next prime is 21957781. The reversal of 21957779 is 97775912.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21957779 - 2⁴ = 21957763 is a prime.

It is a super-2 number, since 2×21957779² = 964288117225682, which contains 22 as substring.

Together with 21957781, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21957799) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10978889 + 10978890.

It is an arithmetic number, because the mean of its divisors is an integer number (10978890).

Almost surely, 2^21957779 is an apocalyptic number.

21957779 is a deficient number, since it is larger than the sum of its proper divisors (1).

21957779 is an equidigital number, since it uses as much as digits as its factorization.

21957779 is an evil number, because the sum of its binary digits is even.

The product of its digits is 277830, while the sum is 47.

The square root of 21957779 is about 4685.9128246266. The cubic root of 21957779 is about 280.0245684224.

The spelling of 21957779 in words is "twenty-one million, nine hundred fifty-seven thousand, seven hundred seventy-nine".