21351972491 has 2 divisors, whose sum is σ = 21351972492. Its totient is φ = 21351972490.

The previous prime is 21351972461. The next prime is 21351972503. The reversal of 21351972491 is 19427915312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21351972491 - 2¹⁰ = 21351971467 is a prime.

It is not a weakly prime, because it can be changed into another prime (21351972461) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10675986245 + 10675986246.

It is an arithmetic number, because the mean of its divisors is an integer number (10675986246).

Almost surely, 2^21351972491 is an apocalyptic number.

21351972491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21351972491 is an equidigital number, since it uses as much as digits as its factorization.

21351972491 is an evil number, because the sum of its binary digits is even.

The product of its digits is 136080, while the sum is 44.

The spelling of 21351972491 in words is "twenty-one billion, three hundred fifty-one million, nine hundred seventy-two thousand, four hundred ninety-one".