A179797 Numbers not of the form abc + abd + acd + bcd, with 0 < a < b < c < d.
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75
Offset: 1
Links
- T. D. Noe, Table of n, a(n) for n=1..764 (complete sequence)
- MathOverflow, A generalisation of the equation n = ab + ac + bc
Crossrefs
Cf. A027563 (which allows equality)
Programs
-
Mathematica
nn=1000000; lim=Floor[nn^(1/3)]; cnt=Table[0,{nn}]; Do[k1=a*b*c; k2=a*b+a*c+b*c; d=0; While[d++; n=k1+k2*d; n<=nn, If[d!=a && d!=b && d!=c, cnt[[n]]=1]], {a,lim}, {b,a+1,Floor[Sqrt[nn/a]]}, {c,b+1,Floor[nn/a/b]}]; Flatten[Position[cnt,0]]
Comments