27261

Appears in sequences

• a(n) = floor((3rd elementary symmetric function of 2,3,...,n+3)/(2+3+...+n+3)).at n=25A024178
• a(n) = binomial(Fibonacci(n) + 1, 2).at n=13A033192
• Odd triangular numbers with prime indices.at n=23A034954
• Triangular numbers which are the sum of two squares.at n=32A073613
• Triangular numbers which are also happy numbers (cf. A007770).at n=36A076712
• Smith triangular numbers.at n=8A098840
• Triangular numbers for which the sum of the digits is a heptagonal number.at n=27A117312
• Expansion of x^2*(43 -11*x -148*x^2 +23*x^3)/(1 -2*x -7*x^2 +7*x^3 +12*x^4 -2*x^5).at n=7A121957
• Triangular numbers T such that T+10 is the next prime after T.at n=7A129540
• Triangular numbers t such that t+10 is a prime.at n=31A129755
• A binomial recursion : a(n) = q(n) (see formula).at n=6A135075
• Triangular numbers p*(p+1)/2 with p prime such that 1+(number of prime factors of p+1) is prime.at n=22A144549
• Triangular numbers which are sums of three consecutive primes.at n=7A167788
• Pseudoprimes to base 8 that are not squarefree.at n=11A243090