26795

Appears in sequences

• Smallest number whose representation requires n triangular numbers with greedy algorithm; also number of 1-2 rooted trees of height n.at n=5A006893
• a(n) = least k such that 1+2+...+k >= E{1,2,...,n}, where E is the 3rd elementary symmetric function.at n=48A027917
• A list of equal temperaments (equal divisions of the octave) whose nearest scale steps are closer and closer approximations to the ratios of three complementary pairs of simple musical tones: 7/6 and 12/7, 6/5 and 5/3 and 7/5 and 10/7.at n=34A060529
• n*10^2-1, n*10^2-3, n*10^2-7 and n*10^2-9 are all prime.at n=31A064976
• Combinatorial triangle !n. This table read by rows gives the coefficients of general sum formulas of n-th left factorials (A003422). The k-th row (k>=1) contains T(i,k) for i=1 to 2*k and k=1 to n-2, where T(i,k) satisfies !n = n + Sum_{k=1..n-2} Sum_{i=1..2*k} T(i,k) * C(n-k-1,i).at n=23A102639
• Number of partitions of {1...n} containing 2 strings of 3 consecutive integers, where each string is counted within a block and a string of more than 3 consecutive integers are counted three at a time.at n=7A105484
• Numbers k such that 2*k+1, 3*k+2, 4*k+3 and 5*k+4 are primes.at n=25A138700
• Numbers k such that 2^(k+1) == 1 (mod k).at n=24A187787
• Partial sums of the number of active (ON, black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 131", based on the 5-celled von Neumann neighborhood.at n=34A270223
• a(n) is the least k such that in the prime power factorization of k! the exponents of primes p_1, ..., p_n are odd, while the exponent of p_(n+1) is even.at n=11A321362
• Composite numbers k coprime to 8 such that k divides Pell(k - Kronecker(8,k)), Pell = A000129.at n=42A327651
• Composite numbers k coprime to 13 such that k divides A006190(k-Kronecker(13,k)).at n=22A327653
• a(n) = Sum_{j=1..n} Sum_{k=1..n} phi(j*k).at n=21A372633