A256355 - OEIS

%I #25 Apr 09 2024 15:58:40

%S 11233,42241,98281,131239,161953,315151,358135,606553,692263,785851,

%T 1114081,1130419,1525777,1906363,3369313,3403081,3880873,5616721,

%U 6036103,6947611,7253191,7516783,7886593,8799127,8811223,9108289,9113203,9195313,9450361,9600769

%N Composites in base 10 that remain composite in exactly three bases b, 2 <= b <= 10, expansions interpreted as decimal numbers.

%H Sebastian Petzelberger, <a href="/A256355/b256355.txt">Table of n, a(n) for n = 1..10000</a>

%H Carlos Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_024.htm">PP&P Puzzle 24: Primes in several bases</a>

%e 11233 = 324413_5 and 324413_10 is composite; 11233 = 44515_7 and 44515_10 is composite; 11233_10 itself is composite. Interpreted in base 2, 3, 4, 6, 8, and 9 the result is prime. Hence 11233 is in this sequence.

%o (PARI) is(n)=!isprime(n) && sum(b=2,9,isprime(fromdigits(digits(n,b))))==6 \\ _Charles R Greathouse IV_, Apr 23 2015

%Y Cf. A052026, A256350, A256351, A256352, A256353, A256354, A256356, A038537, A052027, A052028, A052029, A052030, A052031, A052032, A052033, A084482, A236356.

%K nonn,base

%O 1,1

%A _Sebastian Petzelberger_, Mar 25 2015