21365513551 has 2 divisors, whose sum is σ = 21365513552. Its totient is φ = 21365513550.

The previous prime is 21365513549. The next prime is 21365513573. The reversal of 21365513551 is 15531556312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21365513551 - 2¹ = 21365513549 is a prime.

Together with 21365513549, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21365513551.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21365513051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10682756775 + 10682756776.

It is an arithmetic number, because the mean of its divisors is an integer number (10682756776).

Almost surely, 2^21365513551 is an apocalyptic number.

21365513551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21365513551 is an equidigital number, since it uses as much as digits as its factorization.

21365513551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 67500, while the sum is 37.

The spelling of 21365513551 in words is "twenty-one billion, three hundred sixty-five million, five hundred thirteen thousand, five hundred fifty-one".