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A133958
Home primes whose homeliness is 2.
12
37, 227, 229, 233, 241, 257, 271, 277, 283, 313, 317, 331, 347, 353, 359, 367, 383, 397, 523, 541, 557, 577, 719, 743, 761, 797, 1117, 1171, 1361, 1367, 1373, 1723, 1741, 1747, 1753, 1759, 1783, 1789, 1973, 1979, 1997, 2113, 2131, 2137, 2179, 2213, 2239
OFFSET
1,1
COMMENTS
Number of terms < 10^n: 0, 1, 26, 182, 1428, 10395, 84164, ... .
EXAMPLE
Only {21 & 37} -> 37, etc.
MATHEMATICA
lst = {}; f[n_] := FromDigits@ Flatten[ IntegerDigits@ Table[ #[[1]], {#[[2]]}] & /@ FactorInteger@n, 2]; h[n_] := NestWhileList[f@# &, n, !PrimeQ@# &, 1, 28]; Do[p = h[n][[ -1]]; If[ PrimeQ@p && p < 10^7 && p != n, Print[{n, p}]; AppendTo[lst, p]], {n, 2, 1000}];
d = 2 - 2; lsu = {}; Do[ If[ lst[[n]] == lst[[n + d]] && lst[[n-1]] != lst[[n]] && lst[[n]] != lst[[n + d + 1]], AppendTo[lsu, lst[[n]]]], {n, 188004 - d - 1}]; Take[ Union@ lsu, 50]
KEYWORD
nonn,base
AUTHOR
Robert G. Wilson v, Sep 30 2007
STATUS
approved