A071116 Least m such that sigma(n + phi(m)) = sigma(phi(m)).

2049, 81, 383, 67, 7, 25, 11, 103, 17, 271, 29, 159, 1416741, 35

Offset

1,1

Comments

a(15), if it exists, is at least 10^8. The sequence then continues 31, 239, 41, 227, 43, 25, 339, 683, 71, 31, 151, 43, 67, 2897, 89, 59, 61, 81, 97, 35, 131, 110039, 461, 69, 103, 31, 123, 87981, 1941, 53, 197, 311, 213, 41, 161, 141, 187, 67, 143, 167, 161, 89, 353, 479, 339, 124809, 339, 61, 143, 79, 233, 6723723, 313, 724747, 97, 113, 211, 863, 281, 131, 343, 121, 569, 59217, 127, 127, 309, 61, 271, 103, 1329, 359, 229, 79, 299, 89, 911, 264263, 575, 14627, 281, 139, 203, 267, 211, ..., . - Robert G. Wilson v, Jun 09 2009

Links

Table of n, a(n) for n=1..14.

Mathematica

a[n_] := For[m=1, True, m++, p=EulerPhi[m]; If[DivisorSigma[1, n+p]==DivisorSigma[1, p], Return[m]]]
f[n_] := Block[{k = 1}, While[ DivisorSigma[1, n + EulerPhi@k] != DivisorSigma[1, EulerPhi@k], k++ ]; k] (* Robert G. Wilson v, Jun 09 2009 *)

Crossrefs

Cf. A000010, A000203.

Sequence in context: A017303 A017423 A017555 * A060949 A230189 A321808

Adjacent sequences: A071113 A071114 A071115 * A071117 A071118 A071119

Keyword

nonn

Author

Jason Earls, May 27 2002

Extensions

Edited by Dean Hickerson, Jun 02 2002

I extended the search from 7*10^7 to 10^8 Robert G. Wilson v, Jun 09 2009

Status

approved