A085988 Triangle of least prime signatures such that T(1,1)= 1; T(r,j) = 2*T(r,j-1) for j>1 and T(r+1,1) is the smallest value in A025487 not appearing on an earlier row.

1, 2, 4, 6, 12, 24, 8, 16, 32, 64, 30, 60, 120, 240, 480, 36, 72, 144, 288, 576, 1152, 48, 96, 192, 384, 768, 1536, 3072, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 180, 360, 720, 1440, 2880, 5760, 11520, 23040, 46080, 210, 420, 840, 1680, 3360, 6720, 13440, 26880, 53760, 107520

Offset: 1

Author

Alford Arnold, Jul 12 2003

Keywords

• easy
• nonn
• tabl

Examples

			The table begins:
   1
   2  4
   6 12  24
   8 16  32  64
  30 60 120 240 480
  36 72 144 288 576 1152
  ...
		

Crossrefs

Cf. A025487, A056153, A062515.

Programs

PARI

isli(n) = if(n==1, return(1)); my(f = factor(n)); f[#f~, 1] == prime(#f~) && vecsort(f[, 2], , 4) == f[, 2]; \\ A025487
findfirst(all, used) = {for (k=1, #all, if (!vecsearch(used, all[k]), return (all[k])););}
tabl(nn) = {all = select(x->isli(x), vector(nn, k, k)); used = []; for (n=1, oo, if (n==1, row = [1], first = findfirst(all, used); if (!first, return); row = vector(n, k, first*2^(k-1))); print(row); used = vecsort(concat(used, row)););} \\ Michel Marcus, Feb 20 2019

Extensions

More terms from Michel Marcus, Feb 20 2019