A067671 The prime factors of n are also prime factors of the decimal encoding (A067599) of the prime factorization of n.

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

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