21215961649 has 9 divisors (see below), whose sum is σ = 21421994113. Its totient is φ = 21011896192.

The previous prime is 21215961623. The next prime is 21215961671. The reversal of 21215961649 is 94616951212.

The square root of 21215961649 is 145657.

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

It can be written as a sum of positive squares in 4 ways, for example, as 2052543025 + 19163418624 = 45305^2 + 138432^2 .

It is not a de Polignac number, because 21215961649 - 2¹⁹ = 21215437361 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21215961599 and 21215961608.

It is not an unprimeable number, because it can be changed into a prime (21215961449) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 16458597 + ... + 16459885.

Almost surely, 2^21215961649 is an apocalyptic number.

21215961649 is the 145657-th square number.

21215961649 is the 72829-th centered octagonal number.

It is an amenable number.

21215961649 is a deficient number, since it is larger than the sum of its proper divisors (206032464).

21215961649 is an frugal number, since it uses more digits than its factorization.

21215961649 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2804 (or 1402 counting only the distinct ones).

The product of its digits is 233280, while the sum is 46.

The spelling of 21215961649 in words is "twenty-one billion, two hundred fifteen million, nine hundred sixty-one thousand, six hundred forty-nine".