20074

Appears in sequences

• Numbers k such that 7*10^k + 4*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=10A103059
• Number of connected outerplanar graphs on n unlabeled nodes.at n=9A111563
• Total number of line segments between points visible to each other in a square n X n lattice.at n=15A141255
• Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, -1, -1), (-1, -1, 1), (-1, 0, 1), (0, 1, 1), (1, 0, -1)}.at n=10A148368
• Abs(square of n-th prime minus cube of n-1).at n=35A151911
• Number T(n,k) of set partitions of [n] having exactly k pairs (m,m+1) such that m+1 is in some block b and m is in block b+1; triangle T(n,k), n>=0, 0<=k<=n-floor((1+sqrt(max(0,8n-7)))/2), read by rows.at n=48A270953
• Number of set partitions of [n] having exactly five pairs (m,m+1) such that m+1 is in some block b and m is in block b+1.at n=3A270959
• a(n) = Sum_{-n<i<n, -n<j<n, gcd{i,j}=2} (n-|i|)*(n-|j|)/8.at n=31A331773
• Composite numbers k such that k-A238525(k) and k+A238525(k) are prime.at n=44A342648
• Indices of records in A347113.at n=28A347308
• Index of first occurrence of n in A348179, or -1 if n never appears.at n=27A349423
• Bisection of main diagonal of A115009.at n=7A358297
• Number of partitions of n with exactly four part sizes.at n=35A365630
• a(n) = Sum_{k=0..floor((2*n+1)/5)} binomial(2*k+1,2*n-5*k+1).at n=23A392487