21533423251 has 2 divisors, whose sum is σ = 21533423252. Its totient is φ = 21533423250.

The previous prime is 21533423237. The next prime is 21533423257. The reversal of 21533423251 is 15232433512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21533423251 is a prime.

It is not a weakly prime, because it can be changed into another prime (21533423257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10766711625 + 10766711626.

It is an arithmetic number, because the mean of its divisors is an integer number (10766711626).

Almost surely, 2^21533423251 is an apocalyptic number.

21533423251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21533423251 is an equidigital number, since it uses as much as digits as its factorization.

21533423251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 21600, while the sum is 31.

Adding to 21533423251 its reverse (15232433512), we get a palindrome (36765856763).

The spelling of 21533423251 in words is "twenty-one billion, five hundred thirty-three million, four hundred twenty-three thousand, two hundred fifty-one".