OFFSET
1,1
COMMENTS
LINKS
Michel Lagneau, Table of n, a(n) for n = 1..2000
EXAMPLE
90 is in the sequence because the common prime distinct divisors between a(2)=60 and a(3)=90 are 2, 3 and 5.
MAPLE
with(numtheory):a0:={2, 3, 5}:lst:={}:
for n from 1 to 100 do:
ii:=0:
for k from 30 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)=3
then
printf(`%d, `, k):lst:=lst union {k}:a0:=lst1:ii:=1:
else
fi:
od:
od:
MATHEMATICA
f[s_List]:=Block[{m=s[[-1]], k=30}, While[MemberQ[s, k]||Intersection[Transpose[FactorInteger[k]][[1]], Transpose[FactorInteger[m]][[1]]]=={}|| Length[Intersection[Transpose[FactorInteger[k]][[1]], Transpose[FactorInteger[m]][[1]]]]!=3, k++]; Append[s, k]]; Nest[f, {30}, 70]
PROG
(PARI) lista(nn) = {a = 30; print1(a, ", "); fa = (factor(a)[, 1])~; va = [a]; k = 0; while (k!= nn, k = 1; while (!((#setintersect(fa, (factor(k)[, 1])~) == 3) && (! vecsearch(va, k))), k++); a = k; print1(a, ", "); fa = (factor(a)[, 1])~; va = vecsort(concat(va, k)); ); } \\ Michel Marcus, Nov 24 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Sep 08 2014
STATUS
approved