18336

Appears in sequences

• Arrays of dumbbells.at n=7A002889
• a(n) = s(1)*t(n) + s(2)*t(n-1) + ... + s(k)*t(n-k+1), where k = [ n/2 ], s = (F(2), F(3), F(4), ...), t = (odd natural numbers).at n=23A025106
• Triangular numbers (A000217) with prime indices.at n=42A034953
• Even triangular numbers with prime indices.at n=22A034955
• Numbers n such that n^1024 + 1 is prime (a generalized Fermat prime).at n=22A057002
• Triangular numbers with sum of digits = 21.at n=15A068131
• Numbers k that divide sigma(k-1)+sigma(k)+sigma(k+1), where sigma() is the "sum of integer divisors" function.at n=4A072188
• Smallest multiple of n-th prime which is == 1 mod (n+1)-st prime.at n=42A073603
• Triangular numbers which are 7-almost primes.at n=9A076581
• Smallest triangular number > 1 and == 1 (mod prime(n)).at n=43A087397
• Triangular numbers m such that A040115(m) is also triangular.at n=22A087597
• Triangular numbers with palindromic indices.at n=28A089717
• Triangle read by rows in which the n-th row contains the n smallest triangular numbers with the least significant digits of the n-th triangular number.at n=31A095225
• a(1) = 1, a(2) = 2; for n >= 2, a(n+1) = a(n) + sum of the unique prime factors of a(n).at n=22A096460
• a(1)=1, a(2)=2; for n >= 2, a(n+1) = a(n) + sum of prime factors of a(n).at n=36A096461
• Triangular numbers for which the sum of the digits is an octagonal number.at n=18A117523
• Hexagonal numbers divisible by 6.at n=32A117794
• Triangular numbers n*(n+1)/2 with n prime and n+1 nonprime.at n=41A144519
• a(n) = ((5 + 2*sqrt(2))*(4 + sqrt(2))^n + (5 - 2*sqrt(2))*(4 - sqrt(2))^n)/2.at n=5A163610
• Numbers k such that phi(phi(k)) = sigma(rad(k)).at n=27A173748