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A102500 Values of n for which the concatenation 7nn7 (from sequence A100897) are primes. 3
15, 18, 19, 34, 36, 39, 48, 52, 57, 60, 67, 75, 79, 81, 85, 96, 97, 1005, 1020, 1030, 1047, 1054, 1062, 1065, 1074, 1084, 1086, 1090, 1096, 1108, 1128, 1152, 1153, 1164, 1171, 1173, 1179, 1182, 1185, 1189, 1213, 1215, 1219, 1228, 1231, 1233, 1257, 1269, 1279 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..49.

EXAMPLE

The number 715157 is prime and corresponds to n=15.

The number 7100510057 is prime and corresponds to n=1005.

MATHEMATICA

fQ[n_] := Block[{id = IntegerDigits[n]}, PrimeQ[ FromDigits[ Join[{7}, id, id, {7}]]]]; Select[ Range[1290], fQ[ # ] &] (* Robert G. Wilson v, Jan 14 2004 *)

CROSSREFS

The full sequence of integers of the form 7nn7 is A100897. The primes that correspond to these values of n are sequence A102501.

Sequence in context: A093812 A159840 A124609 * A067757 A063779 A063781

Adjacent sequences:  A102497 A102498 A102499 * A102501 A102502 A102503

KEYWORD

easy,nonn,base

AUTHOR

Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005

EXTENSIONS

More terms from Robert G. Wilson v, Jan 14 2005

STATUS

approved

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Last modified April 8 03:01 EDT 2020. Contains 333312 sequences. (Running on oeis4.)