31284

Appears in sequences

• Numbers k such that 2k-1 divides 2^k-1.at n=21A081856
• a(n) = (n+1)*(n+2)^2*(n+3)*(n+4)*(4*n^2+15*n+15)/720.at n=7A108682
• Amicable triples: numbers such that sigma(x) = sigma(y) = sigma(z) = x+y+z, x<y<z. We order these triples according to the common value of sigma. Sequence gives y numbers.at n=3A125491
• Indices of the records in the sequence of smallest positive quadratic nonresidues (A053760).at n=11A147971
• 1/4 the number of arrangements of n+1 nonzero numbers x(i) in -n..n with the sum of sign(x(i))*(|x(i)| mod x(i+1)) equal to zero.at n=4A189943
• 1/4 the number of arrangements of n+1 nonzero numbers x(i) in -5..5 with the sum of sign(x(i))*(|x(i)| mod x(i+1)) equal to zero.at n=4A189947
• T(n,k)=1/4 the number of arrangements of n+1 nonzero numbers x(i) in -k..k with the sum of sign(x(i))*(|x(i)| mod x(i+1)) equal to zero.at n=40A189951
• 1/4 the number of arrangements of 6 nonzero numbers x(i) in -n..n with the sum of sign(x(i))*(|x(i)| mod x(i+1)) equal to zero.at n=4A189955
• a(n) = smallest k such that prime(n) is the n-th largest divisor of k.at n=21A226326
• Numbers that belong to at least one amicable tuple.at n=27A255215
• Positive integers n such that n=p+q for some primes p,q with pi(p)*pi(q) = sigma(n).at n=29A273286
• G.f.: Product_{k>=1} (1 + x^k) / (1 - x^(k*(k+1)/2)).at n=37A280422
• Number of compositions of n with no part circularly followed by a divisor or a multiple.at n=33A328599
• Numbers k such that k +- 2 and k +- 3 are all semiprimes.at n=10A382049