|
| |
|
|
A135284
|
|
Sum of staircase twin primes according to the rule: top + bottom - next top.
|
|
0
| |
|
|
3, 1, 7, 7, 19, 25, 49, 43, 97, 79, 127, 121, 169, 187, 169, 217, 211, 259, 253, 277, 277, 409, 403, 403, 475, 541, 583, 595, 625, 511, 799, 817, 799, 835, 745, 1009, 1015, 1039, 1033, 1033, 1075, 1183, 1267, 1279, 1285, 1213, 1405, 1423, 1477, 1369, 1597, 1573
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,1
|
|
|
COMMENTS
| The case for bottom - top + next top produces A006512(n+1), the upper twin primes > 5.
|
|
|
FORMULA
| We list the twin primes in staircase fashion as in A135283. Then a(n) = tl(n) + tu(n) + (-tl(n+1)).
|
|
|
PROG
| (PARI) g(n) = for(x=1, n, y=twinu(x) + twinl(x) - twinl(x+1); print1(y", ")) twinl(n) = / *The n-th lower twin prime. */ { local(c, x); c=0; x=1; while(c<n, if(ispseudoprime(prime(x)+2), c++); x++; ); return(prime(x-1)) } twinu(n) = /* The n-th upper twin prime. */ { local(c, x); c=0; x=1; while(c<n, if(isprime(prime(x)+2), c++); x++; ); return(prime(x)) }
|
|
|
CROSSREFS
| Sequence in context: A188463 A101748 A058606 * A016647 A091039 A120472
Adjacent sequences: A135281 A135282 A135283 * A135285 A135286 A135287
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Cino Hilliard (hillcino368(AT)hotmail.com), Dec 03 2007
|
| |
|
|
