21706423561 has 3 divisors (see below), whose sum is σ = 21706570893. Its totient is φ = 21706276230.

The previous prime is 21706423559. The next prime is 21706423573. The reversal of 21706423561 is 16532460712.

The square root of 21706423561 is 147331.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 21706423561 - 2¹ = 21706423559 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21706423561.

It is not an unprimeable number, because it can be changed into a prime (21706403561) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 73666 + ... + 220996.

It is an arithmetic number, because the mean of its divisors is an integer number (7235523631).

Almost surely, 2^21706423561 is an apocalyptic number.

21706423561 is the 147331-st square number.

21706423561 is the 73666-th centered octagonal number.

It is an amenable number.

21706423561 is a deficient number, since it is larger than the sum of its proper divisors (147332).

21706423561 is an frugal number, since it uses more digits than its factorization.

21706423561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 294662 (or 147331 counting only the distinct ones).

The product of its (nonzero) digits is 60480, while the sum is 37.

The spelling of 21706423561 in words is "twenty-one billion, seven hundred six million, four hundred twenty-three thousand, five hundred sixty-one".