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A169887 Primes in carryless arithmetic mod 10. 9
21, 23, 25, 27, 29, 41, 43, 45, 47, 49, 51, 52, 53, 54, 56, 57, 58, 59, 61, 63, 65, 67, 69, 81, 83, 85, 87, 89, 201, 209, 227, 229, 241, 243, 261, 263, 287, 289, 403, 407, 421, 427, 443, 449, 463, 469, 481, 487, 551, 553, 557, 559, 603, 607, 623, 629, 641, 647, 661, 667, 683, 689, 801, 809, 821, 823, 847, 849, 867, 869, 881, 883 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Define the units in carryless arithmetic mod 10 to be the numbers 1, 3, 7 and 9 (these divide any number). A prime is a number N, not a unit, whose only factorizations are of the form N = u * M, where u is a unit.

There are two types: e-type primes (A163396) and f-type (A169984).

LINKS

N. J. A. Sloane, Table of n, a(n) for n = 1..253560 (All primes with <= 9 digits. Based on T. D. Noe's b-files for A058943 and A058955.)

David Applegate, Marc LeBrun and N. J. A. Sloane, Carryless Arithmetic (I): The Mod 10 Version.

Index entries for sequences related to carryless arithmetic

EXAMPLE

Examples of nonprimes: 2 = 2*51, 4 = 2*2, 10 = 52*85, 11 = 57*83, 101 = 13*17, 102 = 58 * 254 = 502 * 801, 103 = 53 * 251 = 507 * 809, 107 = 53 * 259 = 507 * 801, 108 = 58 * 256 = 502 * 809, 111 = 227 * 553.

CROSSREFS

A169887 = A163396 union A169984.

Cf. A004520, A059729, A168294, A168541, A169885, A169886, A169884, A169903 (primitive primes).

Cf. A169962.

Sequence in context: A324321 A095455 A095451 * A007929 A143712 A163396

Adjacent sequences:  A169884 A169885 A169886 * A169888 A169889 A169890

KEYWORD

nonn,base

AUTHOR

David Applegate, Marc LeBrun and N. J. A. Sloane, Jul 06 2010

STATUS

approved

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Last modified October 22 22:34 EDT 2019. Contains 328335 sequences. (Running on oeis4.)