A277781 a(n) is the least k > n such that n*k or n*k^2 is a cube.
8, 4, 9, 16, 25, 36, 49, 27, 24, 80, 88, 18, 104, 112, 120, 32, 136, 96, 152, 50, 168, 176, 184, 72, 40, 208, 64, 98, 232, 240, 248, 54, 264, 272, 280, 48, 296, 304, 312, 135, 328, 336, 344, 242, 75, 368, 376, 162, 56, 160, 408, 338, 424, 108, 440, 189, 456
Offset: 1
Examples
a(2) = 4 because 2 * 4 = 2^3; a(10) = 80 because 10 * 80^2 = 40^3.
Links
- Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Programs
-
Mathematica
Table[SelectFirst[n + Range[7 + n^2], AnyTrue[Power[#, 1/3] & /@ {n #, n #^2}, IntegerQ] &], {n, 57}] (* Michael De Vlieger, Feb 03 2018 *) -
PARI
a(n)=my(f=factor(n),tf=f,a,b); tf[,2]%=3; b=factorback(tf); tf[,2]=2*f[,2]%3; a=factorback(tf); min((sqrtnint(n\a,3)+1)^3*a, (sqrtnint(n\b,3)+1)^3*b) \\ Charles R Greathouse IV, Oct 31 2016
Comments