A085412 - OEIS

A085412

Numbers n such that concatenation of prime[n] and first digit of prime[n] is prime.

6, 8, 11, 12, 22, 27, 29, 36, 37, 42, 44, 67, 68, 71, 72, 73, 74, 75, 76, 133, 134, 138, 157, 160, 161, 162, 163, 164, 166, 169, 172, 174, 175, 179, 180, 187, 197, 204, 207, 210, 232, 235, 237, 247, 249, 251, 254, 261, 263, 264, 269, 272, 278, 282, 285, 287, 303

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

6 is a term because prime[6]=13 and concatenation of 13 and 1 is prime.

MATHEMATICA

cpfdQ[n_]:=Module[{p=Prime[n]}, PrimeQ[10p+IntegerDigits[p][[1]]]]; Select[ Range[ 400], cpfdQ] (* Harvey P. Dale, Apr 06 2017 *)

CROSSREFS

Cf. A085413, A085414.

Sequence in context: A372416 A184113 A309627 * A228650 A358531 A200722

Adjacent sequences: A085409 A085410 A085411 * A085413 A085414 A085415

KEYWORD

nonn,base

AUTHOR

Zak Seidov, Jun 29 2003

STATUS

approved