21724779397 has 2 divisors, whose sum is σ = 21724779398. Its totient is φ = 21724779396.

The previous prime is 21724779331. The next prime is 21724779409. The reversal of 21724779397 is 79397742712.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19710475236 + 2014304161 = 140394^2 + 44881^2 .

It is a cyclic number.

It is not a de Polignac number, because 21724779397 - 2⁷ = 21724779269 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21724779317) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10862389698 + 10862389699.

It is an arithmetic number, because the mean of its divisors is an integer number (10862389699).

Almost surely, 2^21724779397 is an apocalyptic number.

It is an amenable number.

21724779397 is a deficient number, since it is larger than the sum of its proper divisors (1).

21724779397 is an equidigital number, since it uses as much as digits as its factorization.

21724779397 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9335088, while the sum is 58.

The spelling of 21724779397 in words is "twenty-one billion, seven hundred twenty-four million, seven hundred seventy-nine thousand, three hundred ninety-seven".