A154390 Composites whose largest digit is prime.

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

Offset

1,1

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

Example

12 is a term because it is composite and its largest digit (2) is prime.
15 is a term because it is composite and its largest digit (5) is prime.
20 is a term 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
(Python)
from sympy import isprime
def ok(n): return max(str(n)) in "2357" and not isprime(n)
print([k for k in range(208) if ok(k)]) # Michael S. Branicky, Dec 15 2021

Crossrefs

Subsequence of A117815.

Cf. A000040, A002808, A054055, A155777.

Sequence in context: A196224 A163657 A117815 * A346608 A156683 A050696

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