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

Offset: 1

Author

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

Keywords

• nonn
• base

Examples

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

Links

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

Programs

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 *)

Extensions

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