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A153446
Terms in A046034 which are pairwise products of terms in A046034.
1
25, 35, 75, 225, 275, 375, 525, 575, 2275, 2325, 2555, 2775, 3775, 5575, 5775, 7575, 7725, 7755, 22575, 22725, 23275, 23325, 23725, 25275, 25375, 25575, 25725, 27335, 27375, 27775, 32775, 37275, 37775, 52325, 53325, 55225, 55275, 55575, 57375
OFFSET
1,1
COMMENTS
All terms are = 5 (mod 10).
LINKS
EXAMPLE
25 = 5*5 = A046034(3)*A046034(3) = A046034(7);
35 = 5*7 = A046034(3)*A046034(4) = A046034(11);
75 = 3*25 = A046034(2)*A046034(7) = A046034(19);
225 = 3*75 = A046034(2)*A046034(19) = A046034(23);
275 = 5*55 = A046034(3)*A046034(15) = A046034(35).
MATHEMATICA
Select[Flatten@ Table[FromDigits /@ Tuples[{2, 3, 5, 7}, n], {n, 5}], Function[k, Total@ Map[Times @@ # &, Boole@ Map[Total@ Pick[DigitCount@ #, {1, 0, 0, 1, 0, 1, 0, 1, 1, 1}, 1] == 0 &, Transpose@ {#, k/#} &@ Rest@ Take[#, Ceiling[Length[#]/2]] &@ Divisors@ k, {2}]] > 0]] (* Michael De Vlieger, Sep 19 2016 *)
id[n_]:=IntegerDigits[n]; pQ[n_]:=AllTrue[id[n], PrimeQ];
nQ[n_]:=Select[Times@@@Tuples[Select[Divisors[n], AllTrue[id[#], PrimeQ]&], 2], #==n&]
!={};
Select[Flatten@Table[FromDigits/@Tuples[{2, 3, 5, 7}, n], {n, 5}], pQ[#]&&nQ[#]&] (* Ivan N. Ianakiev, Jul 20 2022 *)
CROSSREFS
Cf. A046034 (numbers with prime digits).
Sequence in context: A046423 A347612 A331808 * A039457 A243749 A331143
KEYWORD
base,nonn
AUTHOR
Zak Seidov, Dec 26 2008
STATUS
approved