123123

Appears in sequences

• Duplicate terms of A007908.at n=2A019524
• Lucky numbers that are concatenations of a number k with itself.at n=15A032650
• Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 1,2,3.at n=5A037610
• Sorted list of strings that can be obtained by starting with 123 and repeatedly doubling any substring in place.at n=28A135475
• Sorted list of primitive strings that can be obtained by starting with 123 and repeatedly doubling any substring in place.at n=3A135479
• a(n) = n base 5, under morphism f(1) = 121, f(2) = 123, f(3) = 141, f(4) = 142, or 0 if n base 5 has a zero.at n=11A137850
• a(n) is the smallest number not already in the sequence, such that the concatenation of all a(n) displays the periodic digit string 1, 2, 3 (and repeat).at n=15A165301
• a(n) = numerator of fraction a/b, where gcd(a, b) = 1, whose decimal representation has the form (1)(2)(3)...(n-1)(n).(1)(2)(3)...(n-1)(n).at n=2A172506
• a(n) = Sum_{k=1..n} F(n mod k) where F = A000045, the Fibonacci numbers.at n=49A198259
• a(n) = 3*a(n-2) - a(n-3) with a(0)=0, a(1)=3, a(2)=0.at n=19A214699
• Non-primitive words on {1,2,3}.at n=24A239018
• 3n concatenated with itself.at n=40A248038
• A double binomial sum.at n=6A249014
• Number of set partitions of [n] with maximal block length multiplicity equal to eight.at n=6A271737
• Squarefree integers m > 1 such that if prime p divides m, then s_p(m) >= p and s_p(m) == 3 (mod p-1), where s_p(m) is the sum of the base p digits of m.at n=16A324405