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A264664 a(1)=210; for n > 1, a(n) is the least integer not occurring earlier such that a(n) shares exactly four distinct prime divisors with a(n-1). 2
210, 420, 630, 840, 1050, 1260, 1470, 1680, 1890, 2100, 2310, 330, 660, 990, 1320, 1650, 1980, 2640, 2970, 3300, 3630, 3960, 4290, 390, 780, 1170, 1560, 1950, 2340, 2730, 546, 1092, 1638, 2184, 3276, 3822, 4368, 4914, 5460, 910, 1820, 3640, 4550, 6370, 7280 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The first odd term is a(47) = 1365. - Michel Marcus, Nov 21 2015

LINKS

Michel Lagneau, Table of n, a(n) for n = 1..2000

EXAMPLE

630 is in the sequence because the common prime distinct divisors between a(2)=420 and a(3)=630 are 2, 3, 5 and 7.

MAPLE

with(numtheory):a0:={2, 3, 5, 7}:lst:={}:

for n from 1 to 100 do:

  ii:=0:

    for k from 210 to 50000 while(ii=0) do:

      y:=factorset(k):n0:=nops(y):lst1:={}:

        for j from 1 to n0 do:

        lst1:=lst1 union {y[j]}:

        od:

         a1:=a0 intersect lst1:

         if {k} intersect lst ={} and a1 <> {} and nops(a1)=4

          then

          printf(`%d, `, k):lst:=lst union {k}:a0:=lst1:ii:=1:

         else

         fi:

      od:

  od:

MATHEMATICA

a = {210}; Do[k = 1; While[Nand[! MemberQ[a, k], Length@ Intersection[First /@ FactorInteger@ a[[n - 1]], First /@ FactorInteger@ k] == 4], k++]; AppendTo[a, k], {n, 2, 45}]; a (* Michael De Vlieger, Nov 21 2015 *)

CROSSREFS

Cf. A246946, A246947.

Sequence in context: A229272 A046402 A258359 * A147571 A254466 A235304

Adjacent sequences:  A264661 A264662 A264663 * A264665 A264666 A264667

KEYWORD

nonn

AUTHOR

Michel Lagneau, Nov 20 2015

STATUS

approved

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Last modified October 23 16:15 EDT 2018. Contains 316529 sequences. (Running on oeis4.)