21530779 has 2 divisors, whose sum is σ = 21530780. Its totient is φ = 21530778.

The previous prime is 21530777. The next prime is 21530797. The reversal of 21530779 is 97703512.

Together with next prime (21530797) 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 21530779 - 2¹ = 21530777 is a prime.

Together with 21530777, it forms a pair of twin primes.

It is a plaindrome in base 16.

It is not a weakly prime, because it can be changed into another prime (21530777) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765389 + 10765390.

It is an arithmetic number, because the mean of its divisors is an integer number (10765390).

Almost surely, 2^21530779 is an apocalyptic number.

21530779 is a deficient number, since it is larger than the sum of its proper divisors (1).

21530779 is an equidigital number, since it uses as much as digits as its factorization.

21530779 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 13230, while the sum is 34.

The square root of 21530779 is about 4640.1270456745. The cubic root of 21530779 is about 278.1975158974.

The spelling of 21530779 in words is "twenty-one million, five hundred thirty thousand, seven hundred seventy-nine".