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 A256355 Composites in base 10 that remain composite in exactly three bases b, 2 <= b <= 10, expansions interpreted as decimal numbers. 2
 11233, 42241, 98281, 131239, 161953, 315151, 358135, 606553, 692263, 785851, 1114081, 1130419, 1525777, 1906363, 3369313, 3403081, 3880873, 5616721, 6036103, 6947611, 7253191, 7516783, 7886593, 8799127, 8811223, 9108289, 9113203, 9195313, 9450361, 9600769 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Sebastian Petzelberger, Table of n, a(n) for n = 1..10000 Carlos Rivera, PP&P Puzzle 24: Primes in several bases EXAMPLE 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. PROG (PARI) is(n)=!isprime(n) && sum(b=2, 9, isprime(fromdigits(digits(n, b))))==6 \\ Charles R Greathouse IV, Apr 23 2015 CROSSREFS Cf. A052026, A256350, A256351, A256352, A256353, A256354, A256356, A038537, A052027, A052028, A052029, A052030, A052031, A052032, A052033, A084482, A236356. Sequence in context: A362446 A271582 A185797 * A135015 A104316 A237171 Adjacent sequences: A256352 A256353 A256354 * A256356 A256357 A256358 KEYWORD nonn,base AUTHOR Sebastian Petzelberger, Mar 25 2015 STATUS approved

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Last modified June 17 03:50 EDT 2024. Contains 373432 sequences. (Running on oeis4.)