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A242956
Consider a number n with m decimal digits. The sequence lists the numbers n having the prefix of length m-1 in the middle of the decimal expansion of prime(n).
1
32, 33, 34, 54, 55, 74, 75, 94, 95, 196, 347, 348, 350, 624, 886, 2517, 3598, 4639, 4640, 4641, 6644, 7629, 8581, 9551, 9552, 19573, 28270, 36699, 53053, 61059, 61060, 69024, 76855, 232398, 303026, 303027, 440999, 642469, 5517973, 11689715, 11689716, 27737957
OFFSET
1,1
COMMENTS
The corresponding primes are 131, 137, 139, 251, 257, 373, 379, 491, 499, 1193, 2341, 2347, 2357, 4621, 6883, 22511, ...
EXAMPLE
2517 is in the sequence because prime(2517) = 22511 and the prefix 251 is in the middle of the decimal expansion of 22511.
11689716 is in the sequence because prime(11689716) = 211689719 and the prefix 1168971 is in the middle of the decimal expansion of 211689719.
MATHEMATICA
lst={}; Do[a=IntegerDigits[Prime[n]]; b=Length[a]; c=IntegerLength[(n-Mod[n, 10])/10]; If[EvenQ[b-c]&&FromDigits[Take[a, {(b-c)/2+1, (b+c)/2}]]==(n-Mod[n, 10])/10, AppendTo[lst, n]], {n, 26, 5*10^7}]; lst
CROSSREFS
Cf. A242957.
Sequence in context: A070625 A115421 A108927 * A085259 A054032 A134843
KEYWORD
nonn,base
AUTHOR
Michel Lagneau, May 27 2014
STATUS
approved