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A256351 Composites in base 10 that remain composite in seven bases b, 2<=b<=10, expansions interpreted as decimal numbers. 3
8, 9, 15, 16, 21, 22, 25, 28, 34, 75, 87, 91, 93, 94, 106, 111, 123, 141, 143, 145, 147, 155, 172, 201, 205, 214, 217, 237, 255, 298, 304, 305, 363, 371, 376, 377, 385, 388, 395, 403, 411, 423, 428, 442, 458, 466, 471, 473, 483, 495 (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

MAPLE

f:= proc(b, x) local L, i;

L:= convert(x, base, b);

isprime(add(10^(i-1)*L[i], i=1..nops(L)))

end proc:

select(t -> not isprime(t) and nops(select(f, [$2..9], t))=2, [$1..1000]); # Robert Israel, Mar 26 2015

MATHEMATICA

fQ[n_] := CompositeQ@ n && Count[ CompositeQ[ FromDigits[ IntegerDigits[n, #]] & /@ Range[2, 9]], True] == 6; Select[ Range@ 500, fQ] (* Robert G. Wilson v, Mar 26 2015 *)

CROSSREFS

Cf. A052026, A256350 - A256356.

Cf. A038537, A052027, A052028, A052029, A052030, A052031, A052032, A084482.

Cf. A052033, A236356.

Sequence in context: A114305 A101765 A306490 * A050688 A134334 A292188

Adjacent sequences:  A256348 A256349 A256350 * A256352 A256353 A256354

KEYWORD

nonn,base

AUTHOR

Sebastian Petzelberger, Mar 25 2015

STATUS

approved

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Last modified May 25 19:58 EDT 2019. Contains 323576 sequences. (Running on oeis4.)