11666721821 has 2 divisors, whose sum is σ = 11666721822. Its totient is φ = 11666721820.

The previous prime is 11666721809. The next prime is 11666721839. The reversal of 11666721821 is 12812766611.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10537022500 + 1129699321 = 102650^2 + 33611^2 .

It is a cyclic number.

It is not a de Polignac number, because 11666721821 - 2¹⁰ = 11666720797 is a prime.

It is a super-2 number, since 2×11666721821² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (11666721881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5833360910 + 5833360911.

It is an arithmetic number, because the mean of its divisors is an integer number (5833360911).

Almost surely, 2^11666721821 is an apocalyptic number.

It is an amenable number.

11666721821 is a deficient number, since it is larger than the sum of its proper divisors (1).

11666721821 is an equidigital number, since it uses as much as digits as its factorization.

11666721821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 48384, while the sum is 41.

The spelling of 11666721821 in words is "eleven billion, six hundred sixty-six million, seven hundred twenty-one thousand, eight hundred twenty-one".