[seqfan] Re: Constants from LambertW-Like Sum

Paul D Hanna pauldhanna at juno.com
Sun Mar 13 01:01:26 CET 2016


SeqFans, 
      Ha!  I should have searched for the constants in OEIS! 
 in OEIS we find L(2) as A106533   
"Rumor's constant: the decimal expansion of the number x defined by x*e^(2-2*x)=1." with a formula 
L(2) = -1/2*LambertW(-2*exp(-2)). 
This reveals that, for the L(t) described in the prior email, 
  
L(t) = LambertW(-t*exp(-t)) / (-t). 
Oh, well, it was fun anyway. 
      Paul 
 
---------- Original Message ----------
From: "Paul D Hanna" <pauldhanna at juno.com>
To: seqfan at list.seqfan.eu
Subject: [seqfan] Re: Constants from LambertW-Like Sum
Date: Sat, 12 Mar 2016 23:38:06 GMT

SeqFans, 
     Now I see that     G(t)  =  1/(1 - t*L(t)). 
 
Thus 
 
Sum_{n>=0} (x + n*t)^n * exp(-n*t) / n!  =  exp(L(t)*x) / (1 - t*L(t)). 
 
It would be interesting to find some series for L(t). 
 
There may be an interesting sequence of coefficients there ... 
      Paul 
  
---------- Original Message ----------
From: "Paul D Hanna" <pauldhanna at juno.com>
To: seqfan at list.seqfan.eu
Subject: [seqfan] Constants from LambertW-Like Sum
Date: Sat, 12 Mar 2016 18:45:17 GMT

Seqfans, 
       Consider the sum:  Sum_{n>=0} (x + n*t)^n * exp(-n*t) / n!.  
 
Given |t| < 1, then we can state 
Sum_{n>=0} (x + n*t)^n * exp(-n*t) / n!  =  exp(x) / (1-t). 
 
At |t| = 1, the sum diverges. 
 
When t > 1, it gets more interesting.  
Then there exists constants G(t) and L(t) such that 
 
Sum_{n>=0} (x + n*t)^n * exp(-n*t) / n!  =  G(t)*exp(L(t)*x). 
 
Can the constants shown below be expressed in terms of known constants? 
 
Better yet, can one express G(t) and L(t) as power series in t? 
  
Thanks, 
      Paul 
 
  
G(2) = 1.6845672714463350452134722396973871593628704792654234507517848011333582370842080440793400444766626526814731886234622...
 
L(2) = 0.20318786997997995383847906206241987910549878759057031750024774415195750759190602488362503616907796429146918701550251...
 
 
G(3) = 1.2173752974813388550690230352826825103985770053682908634477086075465719664539122827500982485397095494328867530512115...L(3) = 0.059520209292640368865602889901838268218039418642295302573380768686261898498160869584771144884053451870133655429314201...
 
 
G(4) = 1.0861414494696269868788602383599505862335331529751516554129481866576941864847947286065657853684889673633249960218319...
 
L(4) = 0.019827401281778414109777161846615944868593157198003867399706248552373587908323560641585849526290852738173568432430490...
 
 
G(5) = 1.0361467763175284763084225313980383045149527406704960464902525946633753598575565828790642008172644807382028152774700...
 
L(5) = 0.0069771536511447392602481737354212111888830026405498054371107710439072024085094055523459098679980783404461187416618236...
 
[END]

--
Seqfan Mailing list - http://list.seqfan.eu/

--
Seqfan Mailing list - http://list.seqfan.eu/


More information about the SeqFan mailing list