21515443361 has 2 divisors, whose sum is σ = 21515443362. Its totient is φ = 21515443360.

The previous prime is 21515443319. The next prime is 21515443381. The reversal of 21515443361 is 16334451512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21054010000 + 461433361 = 145100^2 + 21481^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21515443361 is a prime.

It is not a weakly prime, because it can be changed into another prime (21515443381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10757721680 + 10757721681.

It is an arithmetic number, because the mean of its divisors is an integer number (10757721681).

Almost surely, 2^21515443361 is an apocalyptic number.

It is an amenable number.

21515443361 is a deficient number, since it is larger than the sum of its proper divisors (1).

21515443361 is an equidigital number, since it uses as much as digits as its factorization.

21515443361 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 43200, while the sum is 35.

Adding to 21515443361 its reverse (16334451512), we get a palindrome (37849894873).

The spelling of 21515443361 in words is "twenty-one billion, five hundred fifteen million, four hundred forty-three thousand, three hundred sixty-one".