18763

Appears in sequences

• Indices of triple-safe primes: p=prime(n) is double-safe: q=(p-1)/2, r=(q-1)/2 and s=(r-1)/2 are all prime (and q is double-safe).at n=19A075134
• Semiprimes that are the sum of the first n semiprimes for some n.at n=27A092190
• a(1) = 1, a(2) = 2; for n >= 2, a(n+1) = a(n) + sum of the unique prime factors of a(n).at n=25A096460
• Positive numbers y such that y^2 is of the form x^2+(x+647)^2 with integer x.at n=7A159641
• Values of n such that L(20) and N(20) are both prime, where L(k) = (n^2+n+1)*2^(2*k) + (2*n+1)*2^k + 1, N(k) = (n^2+n+1)*2^k + n.at n=48A227523
• Number of (n+2)X(1+2) 0..3 arrays with every 3X3 subblock row and diagonal sum equal to 2 3 4 6 or 7 and every 3X3 column and antidiagonal sum not equal to 2 3 4 6 or 7.at n=11A252400
• a(n) is the smallest number that belongs simultaneously to the two arithmetic progressions prime(n) + m*prime(n+1) and prime(n+1) + m*prime(n+2), m >= 1, n >= 1.at n=31A319524
• Sum of prime parts, counted without multiplicity, in all compositions of n.at n=13A336579
• Number of integer compositions of n whose leaders of strictly increasing runs are identical.at n=18A374686
• a(n) = p(n)*p(n+1)*(p(n+1) - p(n)) + 1, where p(n) = prime(n).at n=15A383242
• The smallest k >= 0 that can be represented as a linear combination of 1^2, 2^2, ..., n^2 with coefficients +-1 and that cannot be represented using 1^2, 2^2, ..., m^2 with 1<=m<n.at n=40A392127
• Number of vertices in a complete bipartite graph where the n vertices of each part are placed on the vertices, and on opposite sides, of a regular 2n-gon.at n=17A392971