21212138729 has 2 divisors, whose sum is σ = 21212138730. Its totient is φ = 21212138728.

The previous prime is 21212138687. The next prime is 21212138737. The reversal of 21212138729 is 92783121212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17049308329 + 4162830400 = 130573^2 + 64520^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212138729 - 2¹² = 21212134633 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21212138692 and 21212138701.

It is not a weakly prime, because it can be changed into another prime (21212138029) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606069364 + 10606069365.

It is an arithmetic number, because the mean of its divisors is an integer number (10606069365).

Almost surely, 2^21212138729 is an apocalyptic number.

It is an amenable number.

21212138729 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212138729 is an equidigital number, since it uses as much as digits as its factorization.

21212138729 is an evil number, because the sum of its binary digits is even.

The product of its digits is 24192, while the sum is 38.

The spelling of 21212138729 in words is "twenty-one billion, two hundred twelve million, one hundred thirty-eight thousand, seven hundred twenty-nine".