21691967251 has 2 divisors, whose sum is σ = 21691967252. Its totient is φ = 21691967250.

The previous prime is 21691967239. The next prime is 21691967257. The reversal of 21691967251 is 15276919612.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21691967251 - 2⁷ = 21691967123 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21691967195 and 21691967204.

It is not a weakly prime, because it can be changed into another prime (21691967257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10845983625 + 10845983626.

It is an arithmetic number, because the mean of its divisors is an integer number (10845983626).

Almost surely, 2^21691967251 is an apocalyptic number.

21691967251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21691967251 is an equidigital number, since it uses as much as digits as its factorization.

21691967251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 408240, while the sum is 49.

The spelling of 21691967251 in words is "twenty-one billion, six hundred ninety-one million, nine hundred sixty-seven thousand, two hundred fifty-one".