OFFSET
1,13
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
a(n) != 0 if and only if n is a term of A008784. - Joerg Arndt, Apr 27 2020
a(n) = 1 if and only if n is a term of A002522. - Bernard Schott, Apr 27 2020
MATHEMATICA
a[n_] := Module[{r, j, k}, r = Solve[j>0 && k>0 && n k - 1 == j^2, {j, k}, Integers]; If[r === {}, Return[0], Return[k /. (r /. C[1] -> 0) // Min]]]; a[1] = 1;
Array[a, 100] (* Jean-François Alcover, Apr 27 2020 *)
PROG
(Haskell)
a076948 1 = 1
a076948 n = if null qs then 0 else head qs
where qs = filter ((> 0) . a037213 . subtract 1 . (* n)) [1..n]
-- Reinhard Zumkeller, Oct 25 2015
(PARI) a(n) = if (!issquare(Mod(-1, n)), 0, my(k=1); while (!issquare(n*k-1), k++); k); \\ Michel Marcus, Apr 27 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Oct 20 2002
EXTENSIONS
Edited and extended by Robert G. Wilson v, Oct 21 2002
STATUS
approved