|
Search: id:A125002
|
|
|
| A125002 |
|
Let p = prime(n); a(n) = number of primes q with same number of digits as p that can be obtained from p by changing one digit. |
|
+0
1
|
|
| 3, 3, 3, 3, 7, 8, 7, 7, 6, 5, 5, 5, 6, 7, 6, 6, 5, 5, 5, 6, 7, 6, 6, 5, 4, 10, 8, 11, 11, 6, 8, 9, 9, 10, 6, 7, 11, 9, 9, 8, 7, 6, 10, 9, 11, 9, 7, 8, 7, 6, 7, 7, 7, 7, 8, 9, 5, 7, 7, 7, 9, 6, 8, 6, 7, 8, 5, 8, 9, 6, 7, 6, 8, 7, 6, 8, 4, 8, 8, 10, 8, 6, 9, 6, 11, 5, 8, 7, 8, 8, 7, 7, 5, 8, 8, 5, 7, 5, 6, 6
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
EXAMPLE
|
The 5th prime 11 leads to 7 other primes: 13,17,19,31,41,61,71, hence a(5)=7.
a(6)=8, p=13, q={11,17,19,23,43,53,73,83}
a(7)=7, p=17, q={11,13,19,37,47,67,97}
a(8)=7, p=19, q={11,13,17,29,59,79,89}
a(9)=6, p=23, q={29,13,43,53,73,83}
a(10)=5, p=29, q={23,19,59,79,89}
|
|
MAPLE
|
A125002 := proc(n) local p, digs, res, r, d; p := ithprime(n) ; digs := convert(p, base, 10) ; res := 0 ; for d from 1 to nops(digs) do for r from 0 to 9 do if r <> op(d, digs) and ( d <> nops(digs) or r > 0) then q := p-(op(d, digs)-r)*10^(d-1) ; if isprime(q) then res := res+1 ; fi ; fi ; od ; od ; RETURN(res) ; end ; for n from 1 to 100 do printf("%d, ", A125002(n)) ; od ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 13 2007
|
|
CROSSREFS
|
Sequence in context: A079084 A092323 A092531 this_sequence A098528 A078229 A007428
Adjacent sequences: A124999 A125000 A125001 this_sequence A125003 A125004 A125005
|
|
KEYWORD
|
nonn,base
|
|
AUTHOR
|
Zak Seidov, Jan 08 2007
|
|
EXTENSIONS
|
Corrected and extended by Hans Havermann (pxp(AT)rogers.com) and R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 08 2007
|
|
|
Search completed in 0.002 seconds
|
