21111111257 has 2 divisors, whose sum is σ = 21111111258. Its totient is φ = 21111111256.

The previous prime is 21111111247. The next prime is 21111111277. The reversal of 21111111257 is 75211111112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17458601161 + 3652510096 = 132131^2 + 60436^2 .

It is a cyclic number.

It is not a de Polignac number, because 21111111257 - 2²² = 21106916953 is a prime.

It is not a weakly prime, because it can be changed into another prime (21111111247) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10555555628 + 10555555629.

It is an arithmetic number, because the mean of its divisors is an integer number (10555555629).

Almost surely, 2^21111111257 is an apocalyptic number.

It is an amenable number.

21111111257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21111111257 is an equidigital number, since it uses as much as digits as its factorization.

21111111257 is an evil number, because the sum of its binary digits is even.

The product of its digits is 140, while the sum is 23.

Adding to 21111111257 its reverse (75211111112), we get a palindrome (96322222369).

The spelling of 21111111257 in words is "twenty-one billion, one hundred eleven million, one hundred eleven thousand, two hundred fifty-seven".