20716561 has 2 divisors, whose sum is σ = 20716562. Its totient is φ = 20716560.

The previous prime is 20716543. The next prime is 20716573. The reversal of 20716561 is 16561702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20657025 + 59536 = 4545^2 + 244^2 .

It is a cyclic number.

It is not a de Polignac number, because 20716561 - 2²¹ = 18619409 is a prime.

It is not a weakly prime, because it can be changed into another prime (20716541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10358280 + 10358281.

It is an arithmetic number, because the mean of its divisors is an integer number (10358281).

Almost surely, 2^20716561 is an apocalyptic number.

It is an amenable number.

20716561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20716561 is an equidigital number, since it uses as much as digits as its factorization.

20716561 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 28.

The square root of 20716561 is about 4551.5449025578. The cubic root of 20716561 is about 274.6455422205.

The spelling of 20716561 in words is "twenty million, seven hundred sixteen thousand, five hundred sixty-one".