A143482 a(1)=1. For n>1, a(n) = the smallest positive multiple of n such that phi(a(n)) >= phi(a(n-1)), where phi(m) is A000010(m).

1, 2, 3, 4, 5, 12, 7, 16, 27, 50, 33, 72, 39, 56, 45, 64, 51, 108, 57, 100, 105, 154, 115, 288, 125, 286, 243, 392, 203, 690, 217, 416, 363, 544, 455, 864, 407, 836, 663, 1000, 451, 1512, 559, 1276, 1125, 1334, 799, 2256, 931, 2000, 1377, 1924, 1007, 2862, 1375

Offset

1,2

Comments

A143483(n) = phi(a(n)).

A143480 is an analogous sequence but with phi(a(n)) > phi(a(n-1)).

Links

Peter Kagey, Table of n, a(n) for n = 1..10000

Example

a(9) = 27 because:
phi(9) = 6 < 8 = phi(a(8)),
phi(18) = 6 < 8 = phi(a(8)),
phi(27) = 18 >= 8 = phi(a(8)).

Mathematica

a = t = {1}; lim = 55; Do[k = 1; While[EulerPhi[k n] < t[[n - 1]], k++]; AppendTo[a, k n]; AppendTo[t, EulerPhi[k n]], {n, 2, lim}]; a (* Michael De Vlieger, Sep 04 2015 *)

Prog

(PARI) lista(nn) = {print1(a=1, ", "); for (n=2, nn, k = 1; phia = eulerphi(a); while(eulerphi(k*n) < phia, k++); a = k*n; print1(a, ", "); ); } \\ Michel Marcus, Sep 22 2015

Crossrefs

Cf. A000010, A143480, A143483.

Sequence in context: A261863 A327262 A344370 * A193679 A066574 A240304

Adjacent sequences: A143479 A143480 A143481 * A143483 A143484 A143485

Keyword

nonn

Author

Leroy Quet, Aug 19 2008

Extensions

Extended by Ray Chandler, Nov 09 2008

Status

approved