21361721819 has 2 divisors, whose sum is σ = 21361721820. Its totient is φ = 21361721818.

The previous prime is 21361721809. The next prime is 21361721827. The reversal of 21361721819 is 91812716312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21361721819 - 2¹² = 21361717723 is a prime.

It is a super-2 number, since 2×21361721819² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21361721809) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10680860909 + 10680860910.

It is an arithmetic number, because the mean of its divisors is an integer number (10680860910).

Almost surely, 2^21361721819 is an apocalyptic number.

21361721819 is a deficient number, since it is larger than the sum of its proper divisors (1).

21361721819 is an equidigital number, since it uses as much as digits as its factorization.

21361721819 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36288, while the sum is 41.

The spelling of 21361721819 in words is "twenty-one billion, three hundred sixty-one million, seven hundred twenty-one thousand, eight hundred nineteen".