18644

Appears in sequences

• Initial n digits in decimal portion of golden ratio phi = (1 + sqrt 5)/2 form a prime number.at n=6A065868
• Numbers k such that h(k) = h(k-1) + h(k-2), where h(k) = A006577(k) + 1 is the length of the sequence {k, f(k), f(f(k)), ...., 1} in the Collatz (or 3x + 1) problem. (The earliest "1" is meant.)at n=32A078418
• Numbers n such that h(n) = 2 h(n-1) where h(n) is the length of the sequence {n, f(n), f(f(n)), ...., 1} in the Collatz (or 3x + 1) problem. (The earliest "1" is meant.)at n=36A078419
• Number of triangles that can be built from rods with lengths 1,2,...,n by using and concatenating all rods.at n=40A160455
• Number of equivalence classes of compositions of n where two compositions a,b are considered equivalent if the summands of a can be permuted into the summands of b with an even number of transpositions.at n=36A218004
• Let sequence B_n={b_m} be defined by: b_1=prime(n), b_2=prime(n+1); for m>=3, b_m=b_(m-2)+b_(m-1) if b_(m-2)+b_(m-1) is not semiprime, otherwise b_m is the least prime divisor of b_(m-2)+b_(m-1). Then a(n) is the maximal term of sequence B_n, or a(n)=0 if B_n is unbounded.at n=30A221218