21509665907 has 2 divisors, whose sum is σ = 21509665908. Its totient is φ = 21509665906.

The previous prime is 21509665867. The next prime is 21509665937. The reversal of 21509665907 is 70956690512.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21509665907 - 2²⁶ = 21442557043 is a prime.

It is not a weakly prime, because it can be changed into another prime (21509665937) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10754832953 + 10754832954.

It is an arithmetic number, because the mean of its divisors is an integer number (10754832954).

Almost surely, 2^21509665907 is an apocalyptic number.

21509665907 is a deficient number, since it is larger than the sum of its proper divisors (1).

21509665907 is an equidigital number, since it uses as much as digits as its factorization.

21509665907 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1020600, while the sum is 50.

The spelling of 21509665907 in words is "twenty-one billion, five hundred nine million, six hundred sixty-five thousand, nine hundred seven".