|
|
A152014
|
|
Number of n-digit primes whose reversal is a different prime.
|
|
2
|
|
|
0, 8, 28, 204, 1406, 9538, 70474, 535578, 4192024, 33619380, 274890230, 2294771254
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
All terms are even.
|
|
LINKS
|
|
|
EXAMPLE
|
a(1)=0 because there are no 1-digit terms in A006567.
a(2)=8 because there are eight 2-digit terms in A006567: 13,17,31,37,71,73,79,97.
|
|
MATHEMATICA
|
Do[c = 0; p = NextPrime[10^(n - 1) - 1]; n1 = PrimePi[p]; n2 = PrimePi[NextPrime[10^n, -1]] - n1 + 1; Do[id = IntegerDigits[p]; i1 = id[[1]]; If[OddQ[i1] && i1 != 5, p1 = FromDigits[ Reverse[id]]; If[p1 != p, If[PrimeQ[p1], c++ ]]]; p = NextPrime[p], {n2}]; Print[{n, c}], {n, 1, 9}];
|
|
CROSSREFS
|
|
|
KEYWORD
|
more,nonn,base
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|