login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A219604 Smallest prime p such that 2n+1 = 4q + p for some odd prime q, or 0 if no such prime exists. 4

%I

%S 0,0,0,0,3,5,3,5,7,13,3,5,7,17,3,5,7,17,11,13,23,17,3,5,7,41,3,5,7,17,

%T 11,13,23,17,3,5,7,0,3,5,7,17,11,13,23,17,3,5,7,73,11,13,31,17,19,37,

%U 23,41,3,5,7,73,3,5,7,17,11,13,23,17,19,29,23,73,3

%N Smallest prime p such that 2n+1 = 4q + p for some odd prime q, or 0 if no such prime exists.

%C a(38) = 0.

%C Conjecture: except m = 77, all odd number > 9 are of the form m = p + 4*q where p and q are prime numbers.

%H Michel Lagneau, <a href="/A219604/b219604.txt">Table of n, a(n) for n = 1..10000</a>

%p for n from 11 by 2 to 200 do:jj:=0:for j from 1 to 1000 while (jj=0) do:p:=ithprime(j):q:=(n-p)/4:if q> 0 and type(q,prime)=true then jj:=1:printf(`%d, `,p):else fi:od:if jj=0 then printf(`%d, `,0):else fi:od:

%t Table[m=3;While[!(PrimeQ[m]&&(((2*n+1-m)/4)>1)&&PrimeQ[(2*n+1-m)/4]),m=m+2];Print[n," ",m],{n,5,200}]

%Y Cf. A219252, A219254, A103506.

%K nonn

%O 1,5

%A _Michel Lagneau_, Apr 12 2013

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 14 09:51 EST 2019. Contains 329111 sequences. (Running on oeis4.)