920721521 has 2 divisors, whose sum is σ = 920721522. Its totient is φ = 920721520.

The previous prime is 920721517. The next prime is 920721523. The reversal of 920721521 is 125127029.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 643332496 + 277389025 = 25364^2 + 16655^2 .

It is an emirp because it is prime and its reverse (125127029) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 920721521 - 2² = 920721517 is a prime.

Together with 920721523, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (920721523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 460360760 + 460360761.

It is an arithmetic number, because the mean of its divisors is an integer number (460360761).

Almost surely, 2^920721521 is an apocalyptic number.

It is an amenable number.

920721521 is a deficient number, since it is larger than the sum of its proper divisors (1).

920721521 is an equidigital number, since it uses as much as digits as its factorization.

920721521 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2520, while the sum is 29.

The square root of 920721521 is about 30343.3933665963. The cubic root of 920721521 is about 972.8430145856.

The spelling of 920721521 in words is "nine hundred twenty million, seven hundred twenty-one thousand, five hundred twenty-one".