A124371 a(n) is the number of earlier terms a(k) such that a(k)*n is a square.

0, 1, 1, 3, 1, 1, 1, 1, 7, 1, 1, 2, 1, 1, 1, 12, 1, 2, 1, 1, 1, 1, 1, 1, 19, 1, 3, 2, 1, 1, 1, 4, 1, 1, 1, 27, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 38, 4, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 51, 1, 1, 1, 1, 1, 1, 1, 5, 1, 1, 5, 2, 1, 1, 1, 4, 64, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 6, 1, 82, 1, 1

Offset

1,4

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Example

12*a(1) = 0 and 12*a(4) = 36 are the two squares made by multiplying earlier terms with 12. So a(12) = 2.

Mathematica

f[l_List] := Append[l, Length[Select[Sqrt /@ ((Length[l] + 1)*l), IntegerQ]]]; Nest[f, {}, 105] (* Ray Chandler, Oct 29 2006 *)

Prog

(PARI)
up_to = 1001;
prepare_A124371(up_to) = { my(v = vector(up_to), c); v[1] = 0; for(n=2, up_to, c=0; for(k=1, n-1, c += issquare(v[k]*n)); v[n] = c); (v); };
v124371 = prepare_A124371(up_to);
A124371(n) = v124371[n]; \\ Antti Karttunen, Jul 21 2018

Crossrefs

Cf. A124372.

Sequence in context: A220693 A208615 A058663 * A147989 A119329 A334549

Adjacent sequences: A124368 A124369 A124370 * A124372 A124373 A124374

Keyword

easy,nonn

Author

Leroy Quet, Oct 27 2006

Extensions

Extended by Ray Chandler, Oct 29 2006

Status

approved