A154389 Nonprimes whose largest digit is an odd nonprime.

1, 9, 10, 39, 49, 69, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100, 110, 111, 119, 129, 159, 169, 189, 190, 192, 194, 195, 196, 198, 209, 219, 249, 259, 279, 289, 290, 291, 292, 294, 295, 296, 297, 298, 299, 309, 319, 329, 339, 369, 390, 391, 392, 393, 394, 395, 396

Offset

1,2

Comments

I.e., nonprimes whose largest digit is 1 or 9. - Jon E. Schoenfield, Feb 11 2019

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

Example

1 is a term because it is nonprime and its largest digit, 1, is an odd nonprime.
9 is a term because it is nonprime and its largest digit, 9, is an odd nonprime.
10 is a term because it is nonprime and its largest digit, 1, is an odd nonprime.
39 is a term because it is nonprime and its largest digit, 9, is an odd nonprime.

Maple

A141468 := proc(n) option remember; if n <= 3 then op(n, [0, 1, 4]) ; else for a from procname(n-1)+1 do if not isprime(a) then return a; end if; end do: end if; end proc:
A054055 := proc(n) max( op(convert(n, base, 10)) ) ; end proc:
for n from 1 to 500 do c := A141468(n) ; if A054055(c) in {1, 9} then printf("%d, ", c ) ; end if; end do: # R. J. Mathar, May 05 2010

Mathematica

ldQ[n_] := Module[{midn = Max[IntegerDigits[n]]}, OddQ[midn] && !PrimeQ[midn]]
Select[Complement[Range[450], Prime[Range[PrimePi[450]]]], ldQ] (* Harvey P. Dale, Jan 31 2011 *)

Prog

(PARI) isok(n) = !isprime(n) && (d = vecmax(digits(n))) && (d % 2) && ! isprime(d); \\ Michel Marcus, Sep 16 2016

Crossrefs

Cf. A054055 (largest digit).

Cf. A141468 (0 together with the nonprime numbers).

Sequence in context: A289520 A038206 A344132 * A041172 A248353 A156857

Adjacent sequences: A154386 A154387 A154388 * A154390 A154391 A154392

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Jan 08 2009

Extensions

Corrected (69 inserted, 111 inserted, 189 inserted, ...) by R. J. Mathar, May 05 2010

Example section edited by Jon E. Schoenfield, Feb 11 2019

Status

approved