A219252 -id:A219252 - cp's OEIS frontend

A219254 Number of ways to express 2n+1 as p+4q with p, q primes.

0, 0, 0, 0, 0, 1, 1, 2, 1, 2, 1, 2, 3, 2, 1, 4, 2, 2, 2, 3, 2, 2, 2, 2, 4, 4, 1, 4, 4, 3, 3, 3, 3, 3, 3, 4, 4, 5, 0, 5, 7, 3, 3, 6, 3, 5, 3, 5, 4, 6, 2, 3, 6, 2, 5, 6, 3, 5, 5, 4, 6, 6, 3, 5, 7, 3, 4, 8, 3, 5, 5, 3, 4, 7, 3, 6, 6, 5, 5, 8, 4, 3, 8, 4, 5, 8, 1

Offset: 0

Michel Lagneau, Apr 11 2013

nonn

This is related to the conjecture given in A219252.

a(38) = 0 because A219252(38) = 0.

			a(15) = 4 because 31 = 23 + 4*2 = 19 + 4*3 = 11 + 4*5 = 3 + 4*7 with 4 decompositions.

Michel Lagneau, Table of n, a(n) for n = 0..10000

Cf. A046927, A219252.

a[n_] := (ways = 0; Do[p = 2k + 1; q = (n-k)/2; If[PrimeQ[p] && PrimeQ[q], ways++], {k, 1, n}]; ways); Table[a[n], {n, 0, 91}]

Name corrected by Zak Seidov, Apr 14 2013

A219604 Smallest prime p such that 2n+1 = 4q + p for some odd prime q, or 0 if no such prime exists.

Original entry on oeis.org

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

Offset: 1

Michel Lagneau, Apr 12 2013

nonn

a(38) = 0.

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

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

Cf. A219252, A219254, A103506.

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:

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}]

A223174 Smallest prime p such that 2n+1 = p + 8*q for some odd prime q, or 0 if no such prime exists.

Original entry on oeis.org

0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 5, 7, 0, 3, 5, 7, 17, 11, 13, 23, 17, 3, 5, 7, 0, 11, 13, 31, 17, 3, 5, 7, 41, 11, 13, 31, 17, 19, 37, 23, 41, 43, 29, 31, 73, 3, 5, 7, 41, 11, 13, 47, 17, 3, 5, 7, 73, 11, 13, 31, 17, 19, 37, 23, 41, 43, 29, 31, 97, 3, 5, 7, 41

Offset: 0

Michel Lagneau, May 09 2013

nonn

For n > 8, a(12) = a(24) = 0.
The corresponding q = 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 0, 3, 3, 3, 2, 3, 3, 2, 3, 5, 5, 5, 0, 5, 5, 3, 5, 7, 7, 7,... are not always the minimum values. The smallest primes q are in A223175.
Conjecture: except m = 25 and 49, all odd numbers > 17 are of the form m = p + 8*q where p and q are prime numbers.

			a(14) = 5 because, for p=5 the corresponding q=3 and 5+8*3 = 29 is prime.

Michel Lagneau, Table of n, a(n) for n = 0..10000

Cf. A219252, A219254, A219604, A219252, A223175, A103506.

for n from 1 by 2 to 200 do:jj:=0:for j from 1 to 1000 while (jj=0) do:p:=ithprime(j):q:=(n-p)/8: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:

A223175 Smallest prime q such that 2n+1 = p + 8*q for some odd prime p, or 0 if no such prime exists.

Original entry on oeis.org

0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 0, 2, 2, 3, 2, 2, 3, 2, 3, 3, 2, 2, 0, 5, 2, 3, 2, 2, 3, 2, 3, 3, 2, 3, 7, 2, 2, 7, 5, 2, 3, 2, 2, 3, 5, 2, 3, 2, 5, 3, 2, 3, 7, 5, 2, 7, 2, 2, 3, 2, 2, 3, 2, 3, 3, 7, 3, 7, 5, 2, 7, 2, 5, 3, 2, 2, 7, 7, 3, 3, 2, 2, 7, 5, 2

Offset: 0

Michel Lagneau, May 09 2013

nonn

For n > 8, a(12) = a(24) = 0.
The corresponding p: 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 5, 7, 0, 11, 13, 7, 17, 19, 13, 23, 17, 19, 29, 31, 0, 11,... are not always the minimum values. The smallest primes p are in A223174.
Conjecture: except m = 25 and 49, all odd numbers > 17 are of the form m = p + 8*q where p and q are prime numbers.

			a(14) = 2 because, for q=2 the corresponding p=13 and 13+8*2 = 29 is prime.

Michel Lagneau, Table of n, a(n) for n = 0..10000

Cf. A219252, A219254, A219604, A219252, A223174, A103506.

for n from 1 by 2 to 200 do:jj:=0:for j from 1 to 1000 while (jj=0) do:q:=ithprime(j):p:=n-8*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:

A225522 Levy's conjecture and generalization. Irregular triangle read by rows: row n gives all odd numbers T(n,k) > 2^(n+1) + 1 such that T(n,k) = p + q*2^n is impossible, where p and q are prime numbers and k = 1..r.

Original entry on oeis.org

0, 77, 25, 49, 41, 47, 57, 81, 113, 167, 203, 233, 257, 473, 73, 79, 85, 89, 91, 97, 121, 129, 141, 145, 151, 159, 181, 187, 211, 217, 225, 251, 279, 281, 301, 343, 349, 385, 511, 601, 751, 913, 1433, 1681, 1951, 137, 143, 149, 153, 155, 161, 163, 167, 173, 177

Offset: 1

Michel Lagneau, May 09 2013

Levy (1963) conjectured that all odd numbers > 5 can be expressed as the sum of a prime plus twice a prime. This conjecture is a stronger version of the weak Goldbach conjecture and has been verified up to n <= 10^9 (according to MathWorld, Corbit 1999). The conjecture was posed by Emile Lemoine in 1895, but in more recent years came to be attributed to Hyman Levy, who pondered it in 1963.
But, according to the sequences A219604 and A223174, it is possible to suggest that this conjecture is generalizable with other powers of 2: the conjecture 2n+1 = p+2q becomes rightfully the conjecture 2n+1 = p + q*2^n.
Conjecture: for each integer n > 1, all odd numbers > 2^(n+1) + 1 are of the form p + q*2^n, except for a finite set of integers {n_1, n_2,..., n_r}, where p and q are prime numbers.
It is impossible to find odd numbers m < 2^(n+1)+1 such that m = p + q*2^n where p and q are primes because with the smallest values p = 3 and q = 2 then m = 2^(n+1) + 3, hence m > 2^(n+1)+1. But there exists, for each value n > 1 a finite set of odd numbers that are not decomposable into the form p + q*2^n:
For n=1 (Levy's conjecture), all odd number > 2^2+1 = 5 are of the form p+2q, p and q primes;
For n=2 (see A219604 and A219252), except the number 77, all numbers > 2^3+1 = 9 are of the form p+4q, p and q primes;
For n=3 (see A223174 and A223175), except the numbers 25 and 49, all numbers > 2^4+1 = 17 are of the form p+8q, p and q primes.
...............
Rows of the triangle:
n=1 => {0}
n=2 => {77},
n=3 => {25, 49},
n=4 => {41, 47, 57, 81, 113, 167, 203, 233, 257, 473},
n=5 => {73, 79, 85, 89, 91, 97, 121, 129, 141, 145, 151, 159, 181, 187, 211, 217, 225, 251, 279, 281, 301, 343, 349, 385, 511, 601, 751, 913, 1433, 1681, 1951}.

			Row 1 = {0} because there is no odd numbers m > 2^2+1 such that 2n+1 = p+2q is impossible.
Row 2 = {77} because, except 77, there is no other odd numbers m > 2^3+1 such that m = p+4q is impossible.
Row 3 = {25, 49} because, except 25 and 49, there is no other odd numbers m > 2^3+1 such that 2n+1 = p+8q is impossible.

K. Guy, Unsolved Problems in Number Theory New York: Springer-Verlag 2004: C1.

Cf. A046927, A219604, A219252, A223174, A223175.

for m from 1 to 6 do: lst:={}:for n from 1 by 2 to 10000 do:jj:=0:for j from 1 to 5000 while (jj=0) do:q:=ithprime(j):p:=n-(2^m)*q:if p> 0 and type(p, prime)=true  then jj:=1: else fi:od:if jj=0 and n > 2^(m+1)+1 then lst:=lst union {n}:else fi:od: print(lst):od:

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A219254 Number of ways to express 2n+1 as p+4q with p, q primes.

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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.

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A223174 Smallest prime p such that 2n+1 = p + 8*q for some odd prime q, or 0 if no such prime exists.

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A223175 Smallest prime q such that 2n+1 = p + 8*q for some odd prime p, or 0 if no such prime exists.

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A225522 Levy's conjecture and generalization. Irregular triangle read by rows: row n gives all odd numbers T(n,k) > 2^(n+1) + 1 such that T(n,k) = p + q*2^n is impossible, where p and q are prime numbers and k = 1..r.

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