21108315551 has 2 divisors, whose sum is σ = 21108315552. Its totient is φ = 21108315550.

The previous prime is 21108315517. The next prime is 21108315643. The reversal of 21108315551 is 15551380112.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21108315551 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21108311551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10554157775 + 10554157776.

It is an arithmetic number, because the mean of its divisors is an integer number (10554157776).

Almost surely, 2^21108315551 is an apocalyptic number.

21108315551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21108315551 is an equidigital number, since it uses as much as digits as its factorization.

21108315551 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6000, while the sum is 32.

Adding to 21108315551 its reverse (15551380112), we get a palindrome (36659695663).

The spelling of 21108315551 in words is "twenty-one billion, one hundred eight million, three hundred fifteen thousand, five hundred fifty-one".