21299561 has 2 divisors, whose sum is σ = 21299562. Its totient is φ = 21299560.

The previous prime is 21299557. The next prime is 21299591. The reversal of 21299561 is 16599212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11689561 + 9610000 = 3419^2 + 3100^2 .

It is a cyclic number.

It is not a de Polignac number, because 21299561 - 2² = 21299557 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21299591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10649780 + 10649781.

It is an arithmetic number, because the mean of its divisors is an integer number (10649781).

Almost surely, 2^21299561 is an apocalyptic number.

It is an amenable number.

21299561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21299561 is an equidigital number, since it uses as much as digits as its factorization.

21299561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9720, while the sum is 35.

The square root of 21299561 is about 4615.1447431256. The cubic root of 21299561 is about 277.1980797675.

The spelling of 21299561 in words is "twenty-one million, two hundred ninety-nine thousand, five hundred sixty-one".