21493751 has 2 divisors, whose sum is σ = 21493752. Its totient is φ = 21493750.

The previous prime is 21493739. The next prime is 21493789. The reversal of 21493751 is 15739412.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21493751 - 2¹⁰ = 21492727 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21493951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10746875 + 10746876.

It is an arithmetic number, because the mean of its divisors is an integer number (10746876).

Almost surely, 2^21493751 is an apocalyptic number.

21493751 is a deficient number, since it is larger than the sum of its proper divisors (1).

21493751 is an equidigital number, since it uses as much as digits as its factorization.

21493751 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7560, while the sum is 32.

The square root of 21493751 is about 4636.1353517774. The cubic root of 21493751 is about 278.0379457546.

The spelling of 21493751 in words is "twenty-one million, four hundred ninety-three thousand, seven hundred fifty-one".