OFFSET
1,2
COMMENTS
The old entry with this sequence number was a duplicate of A026835.
A063524(a(n)) = 0. - Reinhard Zumkeller, Oct 11 2008
Inverse binomial transform of A006589. - Philippe Deléham, Nov 25 2008
a(n) = maximum value of j, where 1 <= j <= n-1, such that floor(j^2 / n) > 0 for each n.
LINKS
FORMULA
G.f.: x^2*(2-x)/(1-x)^2 . E.g.f.: x*(exp(x)-1). - Philippe Deléham, Nov 25 2008
a(n) = A163300(n)/2. - Juri-Stepan Gerasimov, Aug 14 2009
a(n) = n mod sigma_k(n), where sigma_k is the k divisor sigma function. -Enrique Pérez Herrero, Nov 11 2009
a(n+1) = floor((n+sqrt(n^2+8n))/2). - Philippe Deléham, Oct 03 2011
a(n) = n mod n^2. - Andrew Secunda, Aug 21 2015
MATHEMATICA
A087156[n_] := Mod[n, DivisorSigma[1, n]] (* Enrique Pérez Herrero, Nov 11 2009 *)
Drop[Range[0, 80], {2}] (* Harvey P. Dale, Dec 13 2011 *)
PROG
(PARI) a(n)=n-(n==1) \\ Charles R Greathouse IV, Aug 26 2011
(Magma) [n mod n^2: n in [1..100]]; // Vincenzo Librandi, Aug 22 2015
(Python)
def A087156(n): return n if n>1 else 0 # Chai Wah Wu, Jul 31 2024
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Oct 11 2008
EXTENSIONS
Comment and cross-reference added by Christopher Hunt Gribble, Oct 14 2009, Oct 17 2009
STATUS
approved