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A067671 The prime factors of n are also prime factors of the decimal encoding (A067599) of the prime factorization of n. 0
4, 16, 21, 27, 36, 64, 256, 288, 648, 729, 1024, 1444, 1458, 1764, 1936, 2304, 3125, 4096, 4361, 5184, 6272, 7688, 8277, 9408, 11664, 16384, 18432, 19683, 22472, 22987, 26244, 28125, 29403, 31199, 41472, 43264, 59577, 65536, 67712, 73008 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..40.

EXAMPLE

21 = 3^1 * 7^1 has prime factors 3,7, which are also prime factors of the corresponding decimal encoding 3171 = 3^1 * 7^1 * 151^1.

MATHEMATICA

(*f gives the decimal encoding of the prime factorization of n*) f[n_] := FromDigits[Flatten[IntegerDigits[FactorInteger[n]]]]; (*g gives the list of prime factors of n*) g[n_] := Module[{a, l, t}, a = FactorInteger[n]; l = Length[a]; Table[a[[i]][[1]], {i, 1, l}]];

(*main routine*) j[n] := Module[{l1 = g[n], l2 = g[f[n]]}, (Intersection[l1, l2] == l1)]; Select[Range[2, 10^5], j[ # ] &]

CROSSREFS

Cf. A067599.

Sequence in context: A232400 A345763 A354712 * A227815 A075331 A237878

Adjacent sequences: A067668 A067669 A067670 * A067672 A067673 A067674

KEYWORD

nonn,base

AUTHOR

Joseph L. Pe, Feb 04 2002

STATUS

approved

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Last modified January 27 02:41 EST 2023. Contains 359836 sequences. (Running on oeis4.)