21616216513261 has 2 divisors, whose sum is σ = 21616216513262. Its totient is φ = 21616216513260.

The previous prime is 21616216513211. The next prime is 21616216513267. The reversal of 21616216513261 is 16231561261612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11552691155625 + 10063525357636 = 3398925^2 + 3172306^2 .

It is a cyclic number.

It is not a de Polignac number, because 21616216513261 - 2³¹ = 21614069029613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21616216513267) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10808108256630 + 10808108256631.

It is an arithmetic number, because the mean of its divisors is an integer number (10808108256631).

Almost surely, 2^{21616216513261} is an apocalyptic number.

It is an amenable number.

21616216513261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21616216513261 is an equidigital number, since it uses as much as digits as its factorization.

21616216513261 is an evil number, because the sum of its binary digits is even.

The product of its digits is 155520, while the sum is 43.

Adding to 21616216513261 its reverse (16231561261612), we get a palindrome (37847777774873).

The spelling of 21616216513261 in words is "twenty-one trillion, six hundred sixteen billion, two hundred sixteen million, five hundred thirteen thousand, two hundred sixty-one".