A078150 Smallest k such that d(phi(k)) - phi(d(k)) = n, where d(k) = A000005(k) and phi(k) = A000010(k).

3, 5, 7, 17, 13, 35, 31, 37, 113, 77, 61, 221, 185, 143, 211, 209, 181, 287, 241, 577, 1729, 403, 421, 1297, 1057, 1001, 2113, 779, 1009, 899, 1321, 1917, 5629, 1333, 1801, 2233, 7125, 1763, 2161, 2993, 4433, 4851, 3737, 3311, 51319, 2623, 2521

Offset

1,1

Links

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

Mathematica

f[x_] := DivisorSigma[0, EulerPhi[x]]-EulerPhi[DivisorSigma[0, x]] t=Table[0, {100}]; Do[s=f[n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 100000}]; t

Prog

(PARI) a(n) = my(k=1); while (numdiv(eulerphi(k)) - eulerphi(numdiv(k)) != n, k++); k; \\ Michel Marcus, Jun 19 2025

Crossrefs

Cf. A000005, A000010.

Least inverse of A385122.

Sequence in context: A099863 A112092 A031441 * A276044 A396489 A114265

Adjacent sequences: A078147 A078148 A078149 * A078151 A078152 A078153

Keyword

easy,nonn

Author

Labos Elemer, Nov 26 2002

Status

approved