The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A211996 Number of ordered pairs (i,j) such that i*j=n and i+j is a square. 3
 0, 0, 2, 1, 0, 0, 0, 2, 0, 0, 0, 0, 0, 2, 2, 0, 0, 2, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 2, 0, 4, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 4, 1, 0, 2, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(n)=1 for n>0 in A141046. a(8820)=8 and it is the only term in the first 10000 terms that is greater than 6. There are 977 terms in the first 10000 terms that are greater than zero. - Harvey P. Dale, Nov 08 2012 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 D. Clark, An arithmetical function associated with the rank of elliptic curves, Canad. Math. Bull. Vol. 34 (2), 1991 pp. 181-185. EXAMPLE For n=3, the pairs (a,b) such that a*b=3 are (1,3) and (3,1). Both pairs add up to a square, so a(3) = 2. MATHEMATICA nop[n_]:=Module[{divs=Divisors[n]}, Count[Thread[{divs, Reverse[divs]}], _?(IntegerQ[Sqrt[Total[#]]]&)]]; Array[nop, 90] (* Harvey P. Dale, Nov 08 2012 *) PROG (Haskell) a211996 n = length [x | x <- [1..n], let (y, m) = divMod n x,                         m == 0, a010052 (x + y) == 1] -- Reinhard Zumkeller, Oct 28 2012 (PARI) a(n) = sumdiv(n, d, issquare(d+n/d)); \\ Michel Marcus, Jan 18 2021 CROSSREFS Cf. A010052. Sequence in context: A127841 A091006 A167365 * A227834 A025894 A339087 Adjacent sequences:  A211993 A211994 A211995 * A211997 A211998 A211999 KEYWORD nonn AUTHOR Michel Marcus, Oct 25 2012 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 28 13:47 EST 2021. Contains 349413 sequences. (Running on oeis4.)