A371653 Numbers k such that the number formed by putting the digits of k in descending order is prime.
2, 3, 5, 7, 11, 13, 14, 16, 17, 31, 34, 35, 37, 38, 41, 43, 53, 61, 71, 73, 79, 83, 97, 112, 113, 118, 119, 121, 124, 125, 128, 131, 133, 134, 136, 142, 143, 145, 146, 149, 152, 154, 157, 163, 164, 166, 167, 175, 176, 179, 181, 182, 188, 191, 194, 197, 199
Offset: 1
Examples
142 is a term because its digits in decreasing order form 421 and this is prime.
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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Maple
dd:= proc(n) local L,i; L:= sort(convert(n,base,10)); add(L[i]*10^(i-1),i=1..nops(L)) end proc: select(isprime @ dd, [$1..1000]); # Robert Israel, Apr 01 2024
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Mathematica
Select[Range[500], PrimeQ[FromDigits[ReverseSort[IntegerDigits[#]]]] &]
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Python
from sympy import isprime def ok(n): return isprime(int("".join(sorted(str(n), reverse=True)))) print([k for k in range(200) if ok(k)]) # Michael S. Branicky, Apr 01 2024 -
Python
from itertools import count, islice, combinations_with_replacement from sympy import isprime from sympy.utilities.iterables import multiset_permutations def A371653_gen(): # generator of terms for l in count(1): xlist = [] for p in combinations_with_replacement('987654321',l): if isprime(int(''.join(p))): xlist.extend(int(''.join(d)) for d in multiset_permutations(p)) yield from sorted(xlist) A371653_list = list(islice(A371653_gen(),30)) # Chai Wah Wu, Apr 10 2024
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