login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A061345 Odd prime powers. 25
1, 3, 5, 7, 9, 11, 13, 17, 19, 23, 25, 27, 29, 31, 37, 41, 43, 47, 49, 53, 59, 61, 67, 71, 73, 79, 81, 83, 89, 97, 101, 103, 107, 109, 113, 121, 125, 127, 131, 137, 139, 149, 151, 157, 163, 167, 169, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Let a(n)=p^e, then tau(a(n)^2) = tau(p^(2*e)) = 2*e+1 = 2*(e+1)-1 = tau(2*a(n))-1 where tau=A000005. - Juri-Stepan Gerasimov, Jul 14 2011

LINKS

Robert Israel, Table of n, a(n) for n = 0..10000

L. J. Corwin, Irreducible polynomials over the integers which factor mod p for every p, Unpublished Bell Labs Memo, Sep 07 1967 [Annotated scanned copy]

FORMULA

a(n) = A061344(n)-1.

Intersection of A000961 (prime powers) and A005408 (odd numbers). - Robert Israel, Jun 11 2014

MAPLE

select(t -> nops(ifactors(t)[2])<=1, [seq(2*i+1, i=0..1000)]); # Robert Israel, Jun 11 2014

# alternative:

A061345 := proc(n)

    option remember;

    local k ;

    if n = 0 then

        1;

    else

        for k from procname(n-1)+2 by 2 do

            if nops(numtheory[factorset](k)) = 1 then

                return k ;

            end if;

        end do:

    end if;

end proc: # R. J. Mathar, Jun 25 2016

MATHEMATICA

t={1}; k=0; Do[If[k==1, AppendTo[t, a1]]; k=0; Do[c=Sqrt[a^2+b^2]; If[IntegerQ[c]&&GCD[a, b, c]==1, k++; a1=a; b1=b; c1=c; ], {b, 4, a^2/2, 2}], {a, 3, 260, 2}]; t (* Vladimir Joseph Stephan Orlovsky, Jan 29 2012 *)

Select[2 Range@ 130 - 1, PrimeNu@# < 2 &] (* Robert G. Wilson v, Jun 12 2014 *)

PROG

(MAGMA) [1] cat [n: n in [3..300 by 2] | IsPrimePower(n)]; // Bruno Berselli, Feb 25 2016

(PARI) is(n)=my(p); if(isprimepower(n, &p), p>2, n==1) \\ Charles R Greathouse IV, Jun 08 2016

CROSSREFS

Cf. A061346, A000961, A005408, A061344.

Sequence in context: A112372 A082916 A098903 * A238266 A080429 A050150

Adjacent sequences:  A061342 A061343 A061344 * A061346 A061347 A061348

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Jun 08 2001

EXTENSIONS

More terms from Larry Reeves (larryr(AT)acm.org), Jun 12 2001

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified March 26 18:46 EDT 2017. Contains 284137 sequences.