21171779 has 2 divisors, whose sum is σ = 21171780. Its totient is φ = 21171778.

The previous prime is 21171767. The next prime is 21171797. The reversal of 21171779 is 97717112.

Together with next prime (21171797) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21171779 - 2¹² = 21167683 is a prime.

It is not a weakly prime, because it can be changed into another prime (21171739) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10585889 + 10585890.

It is an arithmetic number, because the mean of its divisors is an integer number (10585890).

Almost surely, 2^21171779 is an apocalyptic number.

21171779 is a deficient number, since it is larger than the sum of its proper divisors (1).

21171779 is an equidigital number, since it uses as much as digits as its factorization.

21171779 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6174, while the sum is 35.

The square root of 21171779 is about 4601.2801479588. The cubic root of 21171779 is about 276.6426380319.

The spelling of 21171779 in words is "twenty-one million, one hundred seventy-one thousand, seven hundred seventy-nine".