19900

Appears in sequences

• a(n) = n^2*(2*n^2 - 1); also Sum_{k=0..n-1} (2k+1)^3.at n=10A002593
• Even triangular numbers with prime indices.at n=23A034955
• Numbers k such that k | sigma_11(k).at n=35A055715
• a(n) = 49*(n*(n+1)/2) + 6.at n=28A061792
• Triangular numbers of the form 10*k.at n=39A069498
• Triangular numbers with internal digits also forming a triangular number.at n=31A069702
• Triangular numbers whose internal digits form a triangular number. Or triangular number such that deleting the MSD and LSD leaves a triangular number.at n=45A077366
• Triangular numbers whose external digits as well as internal digits form triangular numbers.at n=25A077368
• Smallest n-digit triangular number whose external digits as well as internal digits form triangular numbers, or -1 if no such number exists.at n=4A077369
• Sort the digits of these triangular numbers into descending order and drop zeros to get primes.at n=29A082923
• Number of unrooted steric quartic trees with 2n (unlabeled) nodes and possessing a bicentroid; number of 2n-carbon alkanes C(2n)H(4n +2) with a bicentroid when stereoisomers are regarded as different.at n=6A086200
• Transform of n^3 by the Riordan array (1/(1-x^2), x).at n=19A105636
• Triangular numbers all of whose digits are nonprimes.at n=26A111484
• Numbers k such that k = T(x) + T(y) where T(m) is the m-th triangular number and k is concatenate(x, y) in base 10.at n=2A113796
• Triangular numbers whose digit reversal is prime; trailing zeros are permitted.at n=19A115704
• Triangular numbers n divisible by the number of triangular numbers smaller than n.at n=33A117519
• Triangular numbers composed of digits {0,1,9}.at n=7A119047
• Numbers k such that k and k^2 use only the digits 0, 1, 3, 6 and 9.at n=49A136850
• Triangular numbers n*(n+1)/2 with n prime and n+1 nonprime.at n=44A144519
• Totally multiplicative sequence with a(p) = a(p-1) + 9 for prime p.at n=27A166706