21015007121 has 2 divisors, whose sum is σ = 21015007122. Its totient is φ = 21015007120.

The previous prime is 21015007087. The next prime is 21015007163. The reversal of 21015007121 is 12170051012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10746224896 + 10268782225 = 103664^2 + 101335^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21015007121 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21015007093 and 21015007102.

It is not a weakly prime, because it can be changed into another prime (21015007021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10507503560 + 10507503561.

It is an arithmetic number, because the mean of its divisors is an integer number (10507503561).

Almost surely, 2^21015007121 is an apocalyptic number.

It is an amenable number.

21015007121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21015007121 is an equidigital number, since it uses as much as digits as its factorization.

21015007121 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 140, while the sum is 20.

Adding to 21015007121 its reverse (12170051012), we get a palindrome (33185058133).

The spelling of 21015007121 in words is "twenty-one billion, fifteen million, seven thousand, one hundred twenty-one".