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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. 5
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 (list; table; graph; refs; listen; history; text; internal format)
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

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Last modified August 24 16:39 EDT 2019. Contains 326295 sequences. (Running on oeis4.)