A133958 Home primes whose homeliness is 2.

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, ... .

Links

Table of n, a(n) for n=1..47.

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]

Crossrefs

Cf. A037274, A118756, A133957, A133956, A133960, A133962, A133964, A133966, A133968, A133970, A133972, A133974, A133976, A133978.

Sequence in context: A142010 A230006 A284987 * A088544 A051463 A275750

Adjacent sequences: A133955 A133956 A133957 * A133959 A133960 A133961

Keyword

nonn,base

Author

Robert G. Wilson v, Sep 30 2007

Status

approved