A163622 Composite numbers such that the sum of its smallest digit and the largest digit is a prime.
12, 14, 16, 20, 21, 25, 30, 32, 34, 38, 49, 50, 52, 56, 58, 65, 70, 74, 76, 85, 92, 94, 98, 102, 105, 112, 114, 116, 120, 121, 122, 124, 126, 130, 134, 136, 141, 142, 143, 144, 146, 150, 156, 161, 162, 164, 165, 166, 170, 200, 201, 202, 203, 205, 207, 210
Offset: 1
Examples
166 is a composite number whose sum of smallest digit and the largest digit is a prime.
Links
- G. C. Greubel, Table of n, a(n) for n = 1..5000
Programs
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Mathematica
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 *) -
Python
from sympy import isprime def ok(n): digits = list(map(int, str(n))) repdigit, smlg = len(set(digits)) == 1, min(digits) + max(digits) return not repdigit and isprime(smlg) and not isprime(n) print([k for k in range(211) if ok(k)]) # Michael S. Branicky, Dec 14 2021
Extensions
Corrected and extended by Harvey P. Dale, Mar 29 2015
Comments