61512781 has 4 divisors (see below), whose sum is σ = 67104864. Its totient is φ = 55920700.

The previous prime is 61512779. The next prime is 61512809. The reversal of 61512781 is 18721516.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 61512781 - 2¹ = 61512779 is a prime.

It is a super-2 number, since 2×61512781² = 7567644452707922, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (61515781) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2796025 + ... + 2796046.

It is an arithmetic number, because the mean of its divisors is an integer number (16776216).

Almost surely, 2^61512781 is an apocalyptic number.

61512781 is the 3508-th centered decagonal number.

It is an amenable number.

61512781 is a deficient number, since it is larger than the sum of its proper divisors (5592083).

61512781 is a wasteful number, since it uses less digits than its factorization.

61512781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5592082.

The product of its digits is 3360, while the sum is 31.

The square root of 61512781 is about 7843.0084151428. The cubic root of 61512781 is about 394.7496806363.

The spelling of 61512781 in words is "sixty-one million, five hundred twelve thousand, seven hundred eighty-one".