253921

Appears in sequences

• Numbers whose sum of divisors is a sixth power.at n=34A019424
• Numbers that are a product of distinct Mersenne primes (elements of A000668).at n=21A046528
• a(n) = period of x^n + x + 1 over GF(2), i.e., the smallest integer m>0 such that x^n + x + 1 divides x^m + 1 over GF(2).at n=17A046932
• Sum of divisors of n, sigma(n) (A000203), is a power of number of divisors of n, d(n) (A000005).at n=14A051281
• Numbers k such that sigma(usigma(k)) is prime.at n=6A063103
• Numbers n such that sigma(n) is a prime power (A025475).at n=22A065523
• Semiprimes that are a product of Mersenne primes.at n=12A144482
• Semiprimes that are a product of distinct Mersenne primes.at n=8A144856
• Numbers k such that sigma(sigma(k)) is prime.at n=5A247838
• Nonprime numbers k such that sum of the divisors of k is a power of 2.at n=15A254603
• Numbers n such that the number of divisors of sum of divisors of n is prime.at n=33A281882
• a(n) is the largest number k such that sigma(k) = 2^n or 0 if no such k exists.at n=18A295043
• a(1) = 1; for n > 1, a(n) is the smallest number m such that sigma(m) = tau(m)^n or 0 if no such m exists.at n=8A349006
• Irregular table read by rows; the n-th row contains in ascending order the integers m > 1 such that sigma(m) = tau(m)^n; the first row contains 1.at n=19A349838