A087984 9-ish numbers (A011539) which are not lunar primes (A087097).

9, 119, 129, 139, 149, 159, 169, 179, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 229, 239, 249, 259, 269, 279, 289, 290, 291, 292, 293, 294, 295, 296, 297, 298, 299, 339, 349, 359, 369, 379, 389, 390, 391, 392, 393, 394, 395, 396

Offset

1,1

Comments

Three and four digit 9ish numbers are lunar primes iff the smallest digit is strictly smaller than the first and the last digit. This is no longer true from 10109 = 109 x 109 on (where x = lunar product).

Links

M. F. Hasler, Table of n, a(n) for n = 1..10000

D. Applegate, C program for lunar arithmetic and number theory

D. Applegate, M. LeBrun and N. J. A. Sloane, Dismal Arithmetic, preprint, arxiv:1107.1130, July 2011. [Note: we have now changed the name from "dismal arithmetic" to "lunar arithmetic" - the old name was too depressing.]

D. Applegate, M. LeBrun, N. J. A. Sloane, Dismal Arithmetic, J. Int. Seq. 14 (2011) # 11.9.8.

Index entries for sequences related to dismal (or lunar) arithmetic

Formula

A011539 \ A087097. - M. F. Hasler, Nov 19 2018

Prog

From M. F. Hasler, Nov 19 2018: (Start)
(PARI) A087984=setminus(A011539, A087097)
A087984=[9]; for(L=3, 4, forvec(d=vector(L, i, [i==1, 9]), vecmax(d)==9&&vecmin(d)>=min(d[1], d[L])&&A087984=concat(A087984, fromdigits(d)))) \\ terms with < 5 digits
(PARI) is_A087984(n)=vecmax(digits(n))=9&&!is_A087097(n) \\ (End)

Crossrefs

Cf. A011539, A087097. A133626 and A134211 are subsequences.

Sequence in context: A166823 A322928 A340236 * A197544 A234964 A210046

Adjacent sequences: A087981 A087982 A087983 * A087985 A087986 A087987

Keyword

nonn,base

Author

David Applegate and N. J. A. Sloane, Oct 30 2003

Status

approved