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).

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, ...

Links

Table of n, a(n) for n=1..42.

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

Adjacent sequences: A242953 A242954 A242955 * A242957 A242958 A242959

Keyword

nonn,base

Author

Michel Lagneau, May 27 2014

Status

approved