OFFSET
1,2
COMMENTS
First differences give the much older sequence A075568. - N. J. A. Sloane, Sep 26 2006
The n-th prime appears in the sequence of first differences (A075568) not later than at the 2n-th position. To see this it is enough to notice that in the original sequence (excluding the first element) odd and even numbers alternate. Therefore from each odd element m the sequence simply jumps to an even element m+p where p is the smallest previously unused prime. - Max Alekseyev, Sep 26 2006
EXAMPLE
The sequence S is constructed like this:
Start with "1": S = 1, ...
Add the smallest prime not added so far, in order to get a composite:
- Can we add 2? No, because 1+2=3 and 3 is prime.
- Can we add 3? Yes, because 1+3=4 and 4 is composite.
So we now have S = 1,4, ...
Add the smallest prime not added so far in order to get a composite:
- Can we add 2 (smallest available prime)? Yes, because 4+2=6 and 6 is composite.
So we now have S = 1,4,6, ...
- Can we add 5? No, because 6+5=11 and 11 is prime.
- Can we add 7? No, because 6+7=13 and 13 is prime.
- Can we add 11? No, because 6+11=17 and 17 is prime.
- Can we add 13? No, because 6+13=19 and 19 is prime.
- Can we add 17? No, because 6+17=23 and 23 is prime.
- Can we add 19? Yes, because 6+19=25 and 25 is composite.
So we now have S = 1,4,6,25, ...
- Can we add 5 (smallest available prime)? Yes, because 25+5=30 and 30 is composite.
So we now have S = 1,4,6,25,30, ...
etc.
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Eric Angelini, Sep 26 2006
EXTENSIONS
Terms computed by Max Alekseyev
STATUS
approved