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A085520
Numbers whose 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
OFFSET
1,1
LINKS
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
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