21709491761 has 2 divisors, whose sum is σ = 21709491762. Its totient is φ = 21709491760.

The previous prime is 21709491731. The next prime is 21709491787. The reversal of 21709491761 is 16719490712.

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., 21638410000 + 71081761 = 147100^2 + 8431^2 .

It is a cyclic number.

It is not a de Polignac number, because 21709491761 - 2³⁴ = 4529622577 is a prime.

It is a super-2 number, since 2×21709491761² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21709491731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10854745880 + 10854745881.

It is an arithmetic number, because the mean of its divisors is an integer number (10854745881).

Almost surely, 2^21709491761 is an apocalyptic number.

It is an amenable number.

21709491761 is a deficient number, since it is larger than the sum of its proper divisors (1).

21709491761 is an equidigital number, since it uses as much as digits as its factorization.

21709491761 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 190512, while the sum is 47.

The spelling of 21709491761 in words is "twenty-one billion, seven hundred nine million, four hundred ninety-one thousand, seven hundred sixty-one".