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A121083 Number of primitive Pythagorean-like triples a^2+b^2=c^2+k for k=-2 with 0<c<=10^n. 3
3, 19, 182, 1779, 17697, 176794, 1768021, 17676780, 176776851, 1767763756 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

It is conjectured by the first author that a(n)/10^n as n->inf is 1/(4*sqrt(2)) = 0.17677...

LINKS

Table of n, a(n) for n=1..10.

EXAMPLE

a(1)=3 because there are 3 solutions (a,b,c) as (1,1,2), (3,5,6), (7,7,10) with 0<c<=10^1.

MATHEMATICA

countTriples[m_, k_] := Module[ {c2, c2odd, total = 0, fax, g}, Do[ c2 = c^2 + k; If[c2 < 2, Continue[]]; c2odd = c2; While[EvenQ[c2odd], c2odd /= 2]; If [c2odd==1, If [OddQ[Log[2, c2]], total++ ]; Continue[]]; If[Mod[c2odd, 4] == 3, Continue[]]; g = GCD[c2odd, 100947]; If[g != 1 && g^2 != GCD[c2odd, 10190296809], Continue[]]; fax = Map[{Mod[ #[[1]], 4], #[[2]]}&, FactorInteger[c2odd]]; If[Apply[Or, Map[ #[[1]] == 3 && OddQ[ #[[2]]] &, fax]], Continue []]; fax = Cases[fax, {1, aa_}:>aa+1]; fax = Ceiling[Apply[Times, fax]/2]; total += fax; , {c, m}]; total] (* Courtesy of Daniel Lichtblau of Wolfram Research *)

CROSSREFS

Cf. A101931.

Sequence in context: A304578 A303064 A161630 * A213533 A203133 A006531

Adjacent sequences:  A121080 A121081 A121082 * A121084 A121085 A121086

KEYWORD

more,nonn

AUTHOR

Tito Piezas III, Aug 11 2006

EXTENSIONS

First few terms found by Tito Piezas III, James Waldby (j-waldby(AT)pat7.com). Subsequent terms found by Andrzej Kozlowski (akoz(AT)mimuw.edu.pl), Daniel Lichtblau (danl(AT)wolfram.com).

a(8)-a(10) from Hiroaki Yamanouchi, Oct 17 2015

STATUS

approved

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Last modified October 23 14:06 EDT 2018. Contains 316528 sequences. (Running on oeis4.)