A081375 a(n) is the least number k such that A081373(k) = n.

1, 2, 6, 12, 30, 42, 72, 78, 84, 90, 190, 216, 222, 228, 234, 252, 270, 540, 546, 570, 630, 738, 744, 770, 792, 858, 900, 924, 930, 990, 1050, 1638, 1710, 1890, 1980, 2100, 2310, 2418, 2442, 2508, 2562, 2574, 2604, 2700, 2772, 2790, 2850, 2970, 3150

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Mathematica

f[x_] := Count[Table[EulerPhi[j]-EulerPhi[x], {j, 1, x}], 0] t=Table[0, {50}]; Do[s=f[n]; If[s<51&&t[[s]]==0, t[[s]]=n], {n, 1, 4000}]; t

Prog

(PARI) lista(len) = {my(v = vector(len), c = 0, k = 1, i); while(c < len, i = #select(x -> x <= k, invphi(eulerphi(k))); if(i <= len && v[i] == 0, c++; v[i] = k); k++); v; } \\ Amiram Eldar, Nov 08 2024, using Max Alekseyev's invphi.gp

Crossrefs

Cf. A000010, A008479, A081373, A081374, A067004.

Sequence in context: A237704 A181826 A143176 * A024701 A224532 A179674

Adjacent sequences: A081372 A081373 A081374 * A081376 A081377 A081378

Keyword

nonn

Author

Labos Elemer, Mar 24 2003

Status

approved