A256355 Composites in base 10 that remain composite in exactly three bases b, 2 <= b <= 10, expansions interpreted as decimal numbers.

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

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