21565718651 has 2 divisors, whose sum is σ = 21565718652. Its totient is φ = 21565718650.

The previous prime is 21565718593. The next prime is 21565718653. The reversal of 21565718651 is 15681756512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21565718651 - 2¹⁰ = 21565717627 is a prime.

Together with 21565718653, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21565718596 and 21565718605.

It is not a weakly prime, because it can be changed into another prime (21565718653) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10782859325 + 10782859326.

It is an arithmetic number, because the mean of its divisors is an integer number (10782859326).

Almost surely, 2^21565718651 is an apocalyptic number.

21565718651 is a deficient number, since it is larger than the sum of its proper divisors (1).

21565718651 is an equidigital number, since it uses as much as digits as its factorization.

21565718651 is an evil number, because the sum of its binary digits is even.

The product of its digits is 504000, while the sum is 47.

The spelling of 21565718651 in words is "twenty-one billion, five hundred sixty-five million, seven hundred eighteen thousand, six hundred fifty-one".