A362025
a(n) is the least number that reaches 1 after n iterations of the infinitary totient function A064380.
Original entry on oeis.org
2, 3, 4, 5, 9, 11, 16, 17, 28, 29, 46, 47, 99, 145, 167, 205, 314, 397, 437, 793, 851, 1137, 1693, 2453, 2771, 2989, 3701, 5099, 6801, 9299, 12031, 15811, 16816, 21520, 21521, 29547, 39685, 62077, 83191, 103473, 112117, 149535, 157159, 196049, 200267, 303022
Offset: 1
-
infCoprimeQ[n1_, n2_] := Module[{g = GCD[n1, n2]}, If[g == 1, True, AllTrue[FactorInteger[g][[;; , 1]], BitAnd @@ IntegerExponent[{n1, n2}, #] == 0 &]]];
iphi[n_] := Sum[Boole[infCoprimeQ[j, n]], {j, 1, n - 1}];
numiter[n_] := Length@ NestWhileList[iphi, n, # > 1 &] - 1;
seq[kmax_] := Module[{v = {}, n = 1}, Do[If[numiter[k] == n, AppendTo[v, k]; n++], {k, 2, kmax}]; v]; seq[1000]
-
isinfcoprime(n1, n2) = {my(g = gcd(n1, n2), p, e1, e2); if(g == 1, return(1)); p = factor(g)[, 1]; for(i=1, #p, e1 = valuation(n1, p[i]); e2 = valuation(n2, p[i]); if(bitand(e1, e2) > 0, return(0))); 1; }
iphi(n) = sum(j = 1, n-1, isinfcoprime(j, n));
numiter(n) = if(n==2, 1, numiter(iphi(n)) + 1);
lista(kmax) = {my(n = 1); for(k = 2, kmax, if(numiter(k) == n, print1(k, ", "); n++)); }
A364802
Smallest number that reaches 1 after n iterations of the map x -> A356874(x).
Original entry on oeis.org
1, 2, 3, 5, 11, 29, 117, 879, 15279, 963957, 392158939, 2059426052079
Offset: 0
-
f[n_] := f[n] = Module[{d = IntegerDigits[n, 2], nd}, nd = Length[d]; Total[d * Fibonacci[Range[nd, 1, -1]]]]; (* A356874 *)
iternum[n_] := Length@ NestWhileList[f, n, # > 1 &] - 1; (* A364800 *)
seq[kmax_] := Module[{s = {}, imax = -1, i}, Do[i = iternum[k]; If[i > imax, imax = i; AppendTo[s, k]], {k, 1, kmax}]; s]
seq[10^6]
-
f(n) = {my(b = binary(n), nb = #b); sum(i = 1, nb, b[i] * fibonacci(nb - i + 1));} \\ A356874
iternum(n) = if(n == 1, 0, iternum(f(n)) + 1); \\ A364800
lista(kmax) = {my(imax = -1, i1); for(k = 1, kmax, i = iternum(k); if(i > imax, imax = i; print1(k, ", ")));}
A364803
Smallest number that reaches a fixed point after n iterations of the map x -> A022290(x).
Original entry on oeis.org
0, 4, 5, 6, 7, 10, 14, 23, 46, 117, 442, 3006, 47983, 2839934, 918486751, 3769839124330
Offset: 0
-
f[n_] := f[n] = Module[{d = IntegerDigits[n, 2], nd}, nd = Length[d]; Total[d * Fibonacci[Range[nd + 1, 2, -1]]]]; (* A022290 *)
iternum[n_] := -2 + Length@ FixedPointList[f, n]; (* A364801 *)
seq[kmax_] := Module[{s = {}, imax = -1, i}, Do[i = iternum[k]; If[i > imax, imax = i; AppendTo[s, k]], {k, 0, kmax}]; s]
seq[10^6]
-
f(n) = {my(b = binary(n), nb = #b); sum(i = 1, nb, b[i] * fibonacci(nb - i + 2)); } \\ A022290
iternum(n) = if(n < 4, 0, iternum(f(n)) + 1); \\ A364801
lista(kmax) = {my(imax = -1, i1); for(k = 0, kmax, i = iternum(k); if(i > imax, imax = i; print1(k, ", ")));}
A098197
Smallest number m such that the trajectory of m under iteration of cototient function[=A051953] contains exactly n distinct numbers (including m and the fixed point=0). Or: the required number of iterations[=operations,transitions] is n-1.
Original entry on oeis.org
0, 1, 2, 4, 6, 10, 18, 30, 42, 78, 114, 186, 294, 390, 582, 798, 1194, 1950, 2922, 4074, 5586, 7770, 11154, 15810, 22110, 30702, 42570, 53130, 68970, 105090, 159390, 206910, 278850, 361410, 462210, 688722, 1019202, 1389810, 2053770, 3011850
Offset: 1
Trajectories for lengths=n=1,2,3,4 are: {0},{1,0},{2,1,0},{4,2,1,0}
n=15:{390,294,210,162,108,72,48,32,16,8,4,2,1,0}
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