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

1,2

Links

Table of n, a(n) for n=1..55.

Example

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

Prog

(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

Crossrefs

Cf. A025487, A056153, A062515.

Sequence in context: A326489 A217356 A030793 * A073349 A129301 A066523

Adjacent sequences: A085985 A085986 A085987 * A085989 A085990 A085991

Keyword

easy,nonn,tabl

Author

Alford Arnold, Jul 12 2003

Extensions

More terms from Michel Marcus, Feb 20 2019

Status

approved