A163622 - OEIS

%I #14 Dec 14 2021 05:42:47

%S 12,14,16,20,21,25,30,32,34,38,49,50,52,56,58,65,70,74,76,85,92,94,98,

%T 102,105,112,114,116,120,121,122,124,126,130,134,136,141,142,143,144,

%U 146,150,156,161,162,164,165,166,170,200,201,202,203,205,207,210

%N Composite numbers such that the sum of its smallest digit and the largest digit is a prime.

%C Numbers like 111 are ignored, at least two different digits are required.

%H G. C. Greubel, <a href="/A163622/b163622.txt">Table of n, a(n) for n = 1..5000</a>

%e 166 is a composite number whose sum of smallest digit and the largest digit is a prime.

%t comprQ[n_]:=Module[{idn=IntegerDigits[n]},CompositeQ[n]&&Length[Union[ idn]]>1&&PrimeQ[Min[idn]+Max[idn]]]; Select[Range[250],comprQ] (* _Harvey P. Dale_, Mar 29 2015 *)

%o (Python)

%o from sympy import isprime

%o def ok(n):

%o     digits = list(map(int, str(n)))

%o     repdigit, smlg = len(set(digits)) == 1, min(digits) + max(digits)

%o     return not repdigit and isprime(smlg) and not isprime(n)

%o print([k for k in range(211) if ok(k)]) # _Michael S. Branicky_, Dec 14 2021

%Y Cf. A002808, A162658, A141642, A221699.

%K nonn,base

%O 1,1

%A _Parthasarathy Nambi_, Aug 01 2009

%E Corrected and extended by _Harvey P. Dale_, Mar 29 2015