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A085520 Numbers such that the digits alternate between prime and nonprime. 2
12, 13, 15, 17, 20, 21, 24, 26, 28, 29, 30, 31, 34, 36, 38, 39, 42, 43, 45, 47, 50, 51, 54, 56, 58, 59, 62, 63, 65, 67, 70, 71, 74, 76, 78, 79, 82, 83, 85, 87, 92, 93, 95, 97, 120, 121, 124, 126, 128, 129, 130, 131, 134, 136, 138, 139 (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

E.g. 151 is in the sequence as 1 is nonprime and 5 is prime.

MATHEMATICA

dapnQ[n_]:=Module[{c=Boole[PrimeQ[IntegerDigits[n]]], len}, len=Length[c]; c==PadRight[{}, len, {0, 1}]||c==PadRight[{}, len, {1, 0}]]; Select[ Range[ 10, 200], dapnQ] (* Harvey P. Dale, Jul 21 2019 *)

CROSSREFS

Sequence in context: A096514 A074163 A076979 * A085556 A175225 A187234

Adjacent sequences:  A085517 A085518 A085519 * A085521 A085522 A085523

KEYWORD

nonn,base

AUTHOR

Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jul 02 2003

EXTENSIONS

Corrected (120 inserted) by Harvey P. Dale, Jul 21 2019

STATUS

approved

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Last modified December 3 20:09 EST 2021. Contains 349468 sequences. (Running on oeis4.)