21621531656513 has 2 divisors, whose sum is σ = 21621531656514. Its totient is φ = 21621531656512.

The previous prime is 21621531656497. The next prime is 21621531656581. The reversal of 21621531656513 is 31565613512612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17492946556849 + 4128585099664 = 4182457^2 + 2031892^2 .

It is a cyclic number.

It is not a de Polignac number, because 21621531656513 - 2⁴ = 21621531656497 is a prime.

It is not a weakly prime, because it can be changed into another prime (21621530656513) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810765828256 + 10810765828257.

It is an arithmetic number, because the mean of its divisors is an integer number (10810765828257).

Almost surely, 2^{21621531656513} is an apocalyptic number.

It is an amenable number.

21621531656513 is a deficient number, since it is larger than the sum of its proper divisors (1).

21621531656513 is an equidigital number, since it uses as much as digits as its factorization.

21621531656513 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 972000, while the sum is 47.

The spelling of 21621531656513 in words is "twenty-one trillion, six hundred twenty-one billion, five hundred thirty-one million, six hundred fifty-six thousand, five hundred thirteen".