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A225216
Let p = n-th prime. Then a(n) = number of primes generated by prepending to the digits of p the digits of q, where q is any prime less than p.
1
0, 1, 0, 1, 2, 1, 2, 2, 4, 2, 2, 2, 4, 1, 4, 5, 4, 3, 4, 5, 6, 4, 5, 5, 6, 5, 6, 5, 3, 8, 4, 6, 8, 7, 8, 7, 5, 6, 8, 8, 4, 9, 7, 5, 10, 5, 9, 5, 8, 8, 10, 8, 8, 14, 10, 7, 14, 8, 8, 11, 10, 13, 8, 10, 10, 10, 11, 12, 13, 8, 11, 14, 12, 11, 13, 13, 13, 16
OFFSET
1,5
COMMENTS
The graph makes it apparent that there are fewer primes generated when the prime p increases its length from 3 to 4 and 4 to 5 digits. - T. D. Noe, May 03 2013
EXAMPLE
a(2)=1 since second prime 3 generates 23. Also a(7)=2 since for the seventh prime 17 we have two primes 317 and 1117.
MATHEMATICA
con[x_, y_] := FromDigits[Join[IntegerDigits[Prime[x]], IntegerDigits[Prime[y]]]]; t={}; Do[c=0; Do[If[PrimeQ[con[i, n]], c=c+1], {i, n}]; AppendTo[t, c], {n, 78}]; t
CROSSREFS
Sequence in context: A070306 A355639 A050378 * A161833 A294100 A139318
KEYWORD
nonn,base
AUTHOR
Jayanta Basu, May 02 2013
STATUS
approved