login
A376704
4-brilliant numbers: numbers which are the product of four primes having the same number of decimal digits.
6
16, 24, 36, 40, 54, 56, 60, 81, 84, 90, 100, 126, 135, 140, 150, 189, 196, 210, 225, 250, 294, 315, 350, 375, 441, 490, 525, 625, 686, 735, 875, 1029, 1225, 1715, 2401, 14641, 17303, 20449, 22627, 24167, 25289, 26741, 28561, 29887, 30613, 31603, 34969, 35321, 36179
OFFSET
1,1
LINKS
EXAMPLE
35321 is a term because 35321 = 11 * 13 * 13 * 19, and these four prime factors have the same number of digits.
MATHEMATICA
A376704Q[k_] := With[{f = FactorInteger[k]}, Total[f[[All, 2]]] == 4 && Length[Union[IntegerLength[f[[All, 1]]]]] == 1];
Select[Range[40000], A376704Q] (* or *)
dlist4[d_] := Sort[Times @@@ DeleteDuplicates[Map[Sort, Tuples[Prime[Range[PrimePi[10^(d-1)] + 1, PrimePi[10^d]]], 4]]]]; (* Generates terms with d-digits prime factors -- faster but memory intensive *)
Flatten[Array[dlist4, 2]]
CROSSREFS
Subsequence of A014613.
Sequence in context: A323350 A307341 A046370 * A103248 A286195 A140135
KEYWORD
nonn,base
AUTHOR
Paolo Xausa, Oct 02 2024
STATUS
approved