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 A154390 Composites whose largest digit is prime. 2
 12, 15, 20, 21, 22, 25, 27, 30, 32, 33, 35, 45, 50, 51, 52, 54, 55, 57, 70, 72, 74, 75, 76, 77, 102, 105, 112, 115, 117, 120, 121, 122, 123, 125, 130, 132, 133, 135, 145, 147, 150, 152, 153, 154, 155, 170, 171, 172, 174, 175, 176, 177, 200, 201, 202, 203, 205, 207 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS G. C. Greubel, Table of n, a(n) for n = 1..1000 EXAMPLE 12 is in the sequence because it is composite and its largest digit (2) is prime. 15 is in the sequence because it is composite and its largest digit (5) is prime. 20 is in the sequence because it is composite and its largest digit (2) is prime. MAPLE a := proc (n) local nn; nn := convert(n, base, 10): if isprime(n) = false and isprime(max(seq(nn[i], i = 1 .. nops(nn)))) = true then n else end if end proc: seq(a(n), n = 1 .. 220); # Emeric Deutsch, Jan 27 2009 MATHEMATICA Select[Range[250], !PrimeQ[#]&&PrimeQ[Max[IntegerDigits[#]]]&] (* Harvey P. Dale, Dec 20 2012 *) PROG (GAP) A:=Filtered([2..210], n->not IsPrime(n));; B:=List(List(List(List(A, ListOfDigits), Reversed), Set), Reversed);; a:=List(Filtered([1..Length(B)], i->IsPrime(B[i][1])), i->A[i]); # Muniru A Asiru, Feb 10 2019 CROSSREFS Cf. A000040 (primes), A002808 (composites), A054055 (largest digit). Sequence in context: A196224 A163657 A117815 * A156683 A050696 A144266 Adjacent sequences:  A154387 A154388 A154389 * A154391 A154392 A154393 KEYWORD nonn,base AUTHOR Juri-Stepan Gerasimov, Jan 08 2009 EXTENSIONS Corrected by Juri-Stepan Gerasimov, Jan 28 2009 Corrected (added 21) and extended by Emeric Deutsch, Jan 27 2009 STATUS approved

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Last modified September 22 06:08 EDT 2020. Contains 337289 sequences. (Running on oeis4.)