A072416 a(1) = 2; a(n) = half of the a(n-1)-th even nontotient number.

2, 13, 49, 149, 373, 835, 1727, 3383, 6341, 11419, 19966, 34067, 56967, 93578, 151313, 241281, 379934, 591413, 910879, 1389289, 2099905, 3147743, 4682362, 6914234, 10141072, 14779023, 21408820, 30837491, 44179913, 62974570, 89329823

Offset

1,1

Links

Table of n, a(n) for n=1..31.

Formula

a(5) = 373 = 746/2, where 746 is the a(4) = 149th term in A005277.

Mathematica

a = Table[0, {10^6}]; Do[b = EulerPhi[n]/2; If[b < 10^6 + 1, a[[b]] = 1], {n, 1, 2 10^7}]; b = Select[ Range[10^6], a[[ # ]] == 0 &]; c = 2; Do[ Print[c]; c = b[[c]], {n, 0, 17}]

Crossrefs

Cf. A006508, A071255, A005277, A072415.

Sequence in context: A270294 A330539 A005584 * A319759 A254784 A056305

Adjacent sequences: A072413 A072414 A072415 * A072417 A072418 A072419

Keyword

nonn

Author

Labos Elemer, Jun 17 2002

Extensions

Edited by Robert G. Wilson v, Jun 20 2002

a(18)-a(31) from Donovan Johnson, Oct 29 2010

Status

approved