A211375 Semiprimes that have both prime digits (2,3,5,7) and nonprime digits (1,4,6,8,9), without digits "0".

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

Offset

1,1

Comments

This is to semiprimes A001358 as A220488 is to primes A000040.

Links

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

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

Cf. A001358, A220488.

Sequence in context: A280389 A057489 A070811 * A326387 A217078 A138594

Adjacent sequences: A211372 A211373 A211374 * A211376 A211377 A211378

Keyword

nonn,base,easy,less

Author

Jonathan Vos Post, Feb 06 2013

Status

approved