A143480 a(1)=1. a(n) is the smallest positive multiple of n such that phi(a(n)) > phi(a(n-1)), where phi(m) is A000010(m).

1, 4, 9, 16, 25, 72, 49, 104, 81, 160, 121, 348, 143, 322, 285, 352, 221, 648, 323, 800, 567, 814, 437, 1272, 575, 1066, 729, 1204, 667, 2370, 713, 1376, 1221, 1598, 1225, 2592, 1073, 2242, 1833, 2840, 1271, 4326, 1333, 2816, 2565, 2806, 1457, 4272, 1813

Offset

1,2

Links

Ivan Neretin and Peter Kagey, Table of n, a(n) for n = 1..10000, first 1000 terms from Ivan Neretin.

Maple

n:= 1: A[1]:= 1:
p:= 1:
for n from 2 to 100 do
  for k from ceil(p/n)*n by n do
     r:= numtheory:-phi(k);
     if r > p then
        A[n]:= k;
        p:= r;
        break
     fi
  od:
od:
seq(A[i], i=1..100); # Robert Israel, Sep 04 2015

Mathematica

a = b = {1}; Do[k = 1; While[(r = EulerPhi[nxt = k*n]) <= b[[-1]], k++]; AppendTo[a, nxt]; AppendTo[b, r], {n, 2, 49}]; a (* Ivan Neretin, May 25 2015 *)
FoldList[Block[{e = EulerPhi@ #1, k = 1, m}, While[EulerPhi[Set[m, k #2]] <= e, k++]; m] &, Range@ 49] (* Michael De Vlieger, Aug 29 2017 *)

Crossrefs

Cf. A000010, A143481 (phi(a(n))), A143482 (similar, with >= rather than >), A259439 (a(n)/n).

Sequence in context: A279096 A299153 A133900 * A230365 A274963 A353387

Adjacent sequences: A143477 A143478 A143479 * A143481 A143482 A143483

Keyword

nonn

Author

Leroy Quet, Aug 19 2008

Extensions

Extended by Ray Chandler, Nov 09 2008

Status

approved