21726

Appears in sequences

• Numbers k such that phi(k) is equal to A008473(k-1).at n=6A039780
• Pseudo-random numbers: MS C 6.0 version.at n=31A084275
• Group the natural numbers such that the n-th group sum is divisible by prime(n): (1, 2, 3), (4, 5), (6, 7, 8, 9), (10, 11), (12, 13, 14, 15, 16, 17, 18, 19, 20, 21), ... Sequence contains the sum of the terms in the n-th group.at n=19A086491
• If p(x) is the x-th prime, then the n-th set of 4 consecutive sexy prime pairs starts at p(a(n)).at n=28A095963
• Numbers k such that 3*10^k + 7*R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=11A102977
• Numbers n with property that n+41, n^2+41 and n^3+41 are all primes.at n=13A175260
• Triangle read by rows. T(n, k) = coefficient of x^n in the Taylor expansion of [((1 - x - 2*x^2 - sqrt(1 - 2*x - 3*x^2))/(2*x^2))]^k.at n=57A202710
• Base-6 analog of A208059.at n=66A212995
• Triangle read by rows: T(n,k) = number of plateau polycubes of width n and volume k.at n=58A232483
• Positive integers m such that (m+4)^3 - m^3 is a square.at n=6A263942
• Perimeters of nondegenerate triangles with integer areas, whose side lengths are triangular numbers.at n=40A385737