A280032 Composite numbers n such that the number of digits in n equals the total number of digits in the prime power factorization of n.
10, 14, 15, 16, 21, 25, 27, 32, 35, 49, 64, 81, 105, 106, 111, 112, 115, 118, 119, 121, 122, 123, 129, 133, 134, 135, 141, 142, 145, 146, 147, 155, 158, 159, 160, 161, 162, 166, 169, 175, 177, 178, 183, 185, 189, 192, 194, 201, 203, 205, 213, 215, 217, 219, 224, 235, 237, 245, 249, 250
Offset: 1
Examples
10 = 2*5 is a term (both have 2 digits). 27 = 3^3 is a term (both have 2 digits).
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..5100
Crossrefs
Cf. A279070.
Programs
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Mathematica
ndf[n_]:=Total[IntegerLength/@Select[Flatten[FactorInteger[n]],#!=1&]]; Select[Range[250],!PrimeQ[#]&&IntegerLength[#]==ndf[#]&] (* Ivan N. Ianakiev, Dec 28 2016 *)
Extensions
a(14)-a(60) from Ivan N. Ianakiev, Dec 28 2016
Comments