21123779 has 2 divisors, whose sum is σ = 21123780. Its totient is φ = 21123778.

The previous prime is 21123761. The next prime is 21123841. The reversal of 21123779 is 97732112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21123779 - 2⁸ = 21123523 is a prime.

It is not a weakly prime, because it can be changed into another prime (21123709) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561889 + 10561890.

It is an arithmetic number, because the mean of its divisors is an integer number (10561890).

Almost surely, 2^21123779 is an apocalyptic number.

21123779 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123779 is an equidigital number, since it uses as much as digits as its factorization.

21123779 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5292, while the sum is 32.

The square root of 21123779 is about 4596.0612485040. The cubic root of 21123779 is about 276.4334146373.

The spelling of 21123779 in words is "twenty-one million, one hundred twenty-three thousand, seven hundred seventy-nine".