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A219604 Smallest prime p such that 2n+1 = 4q + p for some odd prime q, or 0 if no such prime exists. 4
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, 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, 23, 41, 3, 5, 7, 73, 3, 5, 7, 17, 11, 13, 23, 17, 19, 29, 23, 73, 3 (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

MAPLE

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:

MATHEMATICA

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}]

CROSSREFS

Cf. A219252, A219254, A103506.

Sequence in context: A249384 A228446 A188889 * A296489 A253398 A151568

Adjacent sequences:  A219601 A219602 A219603 * A219605 A219606 A219607

KEYWORD

nonn

AUTHOR

Michel Lagneau, Apr 12 2013

STATUS

approved

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Last modified October 21 11:40 EDT 2019. Contains 328296 sequences. (Running on oeis4.)