|
| |
|
|
A071390
|
|
Least number m such that Sigma[m]-Phi[m]=n.
|
|
0
| |
|
|
0, 2, 0, 0, 4, 0, 9, 0, 0, 6, 8, 0, 0, 10, 49, 15, 0, 14, 0, 21, 0, 27, 16, 12, 0, 22, 169, 33, 0, 26, 0, 39, 18, 20, 289, 65, 0, 34, 361, 51, 0, 38, 0, 28, 0, 0, 32, 95, 0, 46, 0, 24, 0, 45, 0, 115, 0, 0, 841, 161, 0, 58, 961, 30, 0, 62, 81, 63, 0, 0, 0, 155, 50, 40, 1369, 217, 0, 74
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,2
|
|
|
FORMULA
| a(n)=Min{x; A000203(x)-A000010(x)=n} or a(n)=0 if no solution exists.
|
|
|
EXAMPLE
| n=255: a(255)=16129=127^2, sigma[16129]=16257,phi[16129]=16002 16257-16002=255=n. Prime squares are often solutions(4,9,49,169,289,361, etc.)
|
|
|
MATHEMATICA
| f[x_] := DivisorSigma[1, x]-EulerPhi[x] t=Table[0, {100}]; Do[c=f[n]; If[c<101&&t[[c]]==0, t[[c]]=n], {n, 1, 1000}]; t
|
|
|
CROSSREFS
| Cf. A000010, A000203, A065387, A051612, A071391.
Sequence in context: A084658 A137513 A140668 * A061669 A136334 A155039
Adjacent sequences: A071387 A071388 A071389 * A071391 A071392 A071393
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Labos E. (labos(AT)ana.sote.hu), May 23 2002
|
| |
|
|
