1,1

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, ..., . [From Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 09 2009]

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] [From Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 09 2009]

Cf. A000010, A000203.

Sequence in context: A017303 A017423 A017555 this_sequence A060949 A017685 A013959

Adjacent sequences: A071113 A071114 A071115 this_sequence A071117 A071118 A071119

nonn

Jason Earls (zevi_35711(AT)yahoo.com), May 27 2002

Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Jun 02 2002

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