login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A230443
Number of decompositions of 2n into a sum of two primes p2 >= p1 such that the number of runs in binary expansion of p2-p1 is less than or equal to 4
3
1, 1, 1, 2, 1, 2, 2, 2, 2, 3, 3, 3, 2, 3, 2, 4, 4, 2, 3, 4, 3, 4, 5, 4, 2, 5, 3, 4, 6, 3, 4, 6, 2, 5, 6, 5, 4, 7, 3, 5, 7, 5, 4, 9, 3, 4, 6, 3, 5, 8, 3, 6, 7, 5, 5, 10, 4, 5, 8, 3, 3, 10, 2, 6, 7, 6, 3, 8, 7, 7, 10, 6, 5, 12, 3, 7, 10, 5, 5, 10, 1, 6, 10, 7, 4
OFFSET
2,4
COMMENTS
1. This is a tightly intensified version of Goldbach conjecture.
It is hypothesized that except for n=1402 and 27242, all other terms for n > 1 are greater than zero. Sequence tested up to 1 million without other zero elements.
2. The definition of "the number of runs in binary expansion of k" is from A005811.
3. The first difference of this sequence to A002375 is on a(26).
EXAMPLE
n=2, 2n=4, 4=2+2, 2-2=0, A005811(0)=1 < 4, only one decomposition, so a(2)=1;
...
n=5, 2n=10, 10=5+5=3+7, 5-5=0, A005811(0)=1<4, 7-3=4, A005811(4)=2<4, so a(5)=2;
...
n=26, 2n=52, 52=5+47=11+41=23+29. 47-5=42, A005811(42)=6>4 [X]; 41-11=30, A005811(30)=2<4 [v]; 29-23=6, A005811(6)=2<4 [v]; so a(26)=2.
MATHEMATICA
Table[ev=2*seed; ct=0; cp1=seed-1; While[cp1=NextPrime[cp1]; cp1<ev, cp2=ev-cp1; If[PrimeQ[cp2], test=cp1-cp2; rank=Length[Length/@Split[IntegerDigits[test, 2]]]; If
[rank<=4, ct++]]]; ct, {seed, 2, 100}]
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Lei Zhou, Oct 18 2013
STATUS
approved