A219252 - OEIS

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A219252

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

0, 0, 0, 0, 2, 2, 2, 3, 2, 2, 3, 2, 2, 3, 2, 5, 3, 2, 2, 3, 3, 2, 7, 2, 2, 3, 2, 5, 3, 2, 5, 3, 2, 2, 3, 3, 2, 0, 2, 2, 3, 3, 2, 7, 2, 5, 3, 2, 5, 3, 5, 2, 7, 2, 2, 3, 2, 2, 3, 2, 5, 3, 5, 5, 7, 5, 2, 7, 2, 7, 3, 2, 2, 3, 3, 11, 7, 2, 2, 3, 3, 2, 7, 3, 2, 19, 2, 5, 3, 2

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,5

COMMENTS

a(38) = 0.

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

LINKS

Michel Lagneau, Table of n, a(n) for n = 1..10000

EXAMPLE

3 + 4*2 = 11 => a(5) = 2;

5 + 4*2 = 13 => a(6) = 2;

7 + 4*2 = 15 => a(7) = 2;

5 + 4*3 = 17 => a(8) = 3.

MAPLE

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

CROSSREFS

Cf. A195352, A002091, A219254.

Sequence in context: A377758 A195352 A103507 * A290839 A346651 A085694

Adjacent sequences: A219249 A219250 A219251 * A219253 A219254 A219255

KEYWORD

nonn

AUTHOR

Michel Lagneau, Apr 11 2013

STATUS

approved