A154384 Odd nonprimes with odd sum of digits.

1, 9, 21, 25, 27, 45, 49, 63, 65, 69, 81, 85, 87, 111, 115, 117, 119, 133, 135, 153, 155, 159, 171, 175, 177, 195, 201, 203, 205, 207, 209, 221, 225, 243, 245, 247, 249, 261, 265, 267, 285, 287, 289, 315, 319, 333, 335, 339, 351, 355, 357, 371, 375, 377, 391

Offset

1,2

Links

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

Example

1 is an odd nonprime and has an odd sum of digits, so a(1)=1.
9 is an odd nonprime and has an odd sum of digits (and this is not true for any integers between 1 and 9), so a(2)=9.
21 is an odd nonprime, and the sum of its digits (2+1=3) is odd (and this is not true for any integers between 9 and 21), so a(3)=21, etc.
45 is in the sequence because it is odd, it is a nonprime and the sum of its digits (9) is odd. - Emeric Deutsch, Jan 21 2009

Maple

sd := proc (n) options operator, arrow: add(convert(n, base, 10)[j], j = 1 .. nops(convert(n, base, 10))) end proc: a := proc (n) if `mod`(n, 2) = 1 and isprime(n) = false and `mod`(sd(n), 2) = 1 then n else end if end proc: seq(a(n), n = 1 .. 400); # Emeric Deutsch, Jan 21 2009

Mathematica

Select[Complement[Range[1, 501, 2], Prime[Range[PrimePi[501]]]], OddQ[Total[IntegerDigits[#]]]&] (* Harvey P. Dale, Dec 11 2010 *)

Prog

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

Crossrefs

Odd nonprimes in A014076.

Sequence in context: A322336 A327685 A355535 * A327756 A210251 A143791

Adjacent sequences: A154381 A154382 A154383 * A154385 A154386 A154387

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Jan 08 2009

Extensions

Corrected and extended by Emeric Deutsch, Jan 21 2009

Status

approved