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A211375 Semiprimes that have both prime digits (2,3,5,7) and nonprime digits (1,4,6,8,9), without digits "0". 1
15, 21, 26, 34, 38, 39, 51, 58, 62, 65, 74, 82, 85, 87, 93, 95, 115, 121, 122, 123, 129, 133, 134, 142, 143, 145, 155, 158, 159, 177, 178, 183, 185, 187, 213, 214, 215, 217, 218, 219, 221, 226, 247, 249, 254, 259, 262, 265, 267, 274, 278 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
This is to semiprimes A001358 as A220488 is to primes A000040.
LINKS
EXAMPLE
a(1) = 15 because 15 = 3*5 is semiprime, "1" is a nonprime digit, and "5" is a prime digit.
MATHEMATICA
SemiprimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; fQ[n_] := Module[{d = IntegerDigits[n]}, SemiprimeQ[n] && Intersection[d, {2, 3, 5, 7}] != {} && Intersection[d, {1, 4, 6, 8, 9}] != {} && ! MemberQ[d, 0]]; Select[Range[278], fQ] (* T. D. Noe, Feb 09 2013 *)
spQ[n_]:=PrimeOmega[n]==2&&FreeQ[IntegerDigits[n], 0]&&Count[ IntegerDigits[ n], _?PrimeQ]>0&&Count[IntegerDigits[n], _?(!PrimeQ[#]&)]>0; Select[ Range[ 300], spQ] (* Harvey P. Dale, Mar 31 2022 *)
CROSSREFS
Sequence in context: A280389 A057489 A070811 * A326387 A217078 A138594
KEYWORD
nonn,base,easy,less
AUTHOR
Jonathan Vos Post, Feb 06 2013
STATUS
approved

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Last modified July 12 19:59 EDT 2024. Contains 374252 sequences. (Running on oeis4.)