21555616249 has 2 divisors, whose sum is σ = 21555616250. Its totient is φ = 21555616248.

The previous prime is 21555616211. The next prime is 21555616267. The reversal of 21555616249 is 94261655512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20661187600 + 894428649 = 143740^2 + 29907^2 .

It is a cyclic number.

It is not a de Polignac number, because 21555616249 - 2⁹ = 21555615737 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21555616199 and 21555616208.

It is not a weakly prime, because it can be changed into another prime (21555616279) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10777808124 + 10777808125.

It is an arithmetic number, because the mean of its divisors is an integer number (10777808125).

Almost surely, 2^21555616249 is an apocalyptic number.

It is an amenable number.

21555616249 is a deficient number, since it is larger than the sum of its proper divisors (1).

21555616249 is an equidigital number, since it uses as much as digits as its factorization.

21555616249 is an evil number, because the sum of its binary digits is even.

The product of its digits is 648000, while the sum is 46.

The spelling of 21555616249 in words is "twenty-one billion, five hundred fifty-five million, six hundred sixteen thousand, two hundred forty-nine".