A085520 - OEIS

A085520

Numbers whose digits alternate between prime and nonprime.

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

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OFFSET

1,1

LINKS

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

EXAMPLE

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: A074163 A076979 A365589 * 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