A102500 - OEIS

A102500

Values of n for which the concatenation 7nn7 (from sequence A100897) are primes.

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

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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 A125006

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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