21240290820961 has 9 divisors (see below), whose sum is σ = 21384491196243. Its totient is φ = 21097056443160.

The previous prime is 21240290820949. The next prime is 21240290820967. The reversal of 21240290820961 is 16902809204212.

The square root of 21240290820961 is 4608719.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 2488446305361 + 18751844515600 = 1577481^2 + 4330340^2 .

It is not a de Polignac number, because 21240290820961 - 2⁴¹ = 19041267565409 is a prime.

It is a super-2 number, since 2×21240290820961² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21240290820967) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 686683666 + ... + 686714596.

Almost surely, 2^{21240290820961} is an apocalyptic number.

21240290820961 is the 4608719-th square number.

21240290820961 is the 2304360-th centered octagonal number.

It is an amenable number.

21240290820961 is a deficient number, since it is larger than the sum of its proper divisors (144200375282).

21240290820961 is an frugal number, since it uses more digits than its factorization.

21240290820961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62160 (or 31080 counting only the distinct ones).

The product of its (nonzero) digits is 248832, while the sum is 46.

The spelling of 21240290820961 in words is "twenty-one trillion, two hundred forty billion, two hundred ninety million, eight hundred twenty thousand, nine hundred sixty-one".