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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.)