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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A228122 Smallest nonnegative number x such that x^2 + x + 41 has exactly n prime factors counting multiplicities. 4
0, 40, 420, 1721, 14144, 139563, 3019035, 24304266, 206583092, 3838101265 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..10.

EXAMPLE

a(1) = 0 because if x = 0 then x^2 + x + 41 = 41, which has 1 prime factor.

a(2) = 40 because if x = 40 then x^2 + x + 41 = 1681 = 41*41, which has 2 prime factors, counting multiplicities.

a(3) = 420 because if x = 420 then x^2 + x + 41 = 176861 = 47*53*71, which has 3 prime factors.

MATHEMATICA

a = {}; Do[x = 0; While[PrimeOmega[x^2 + x + 41] != k, x++]; AppendTo[a, x], {k, 9}]; a

PROG

(PARI) a(n) = {my(m=0); while (bigomega(m^2+m+41) != n, m++); m; } \\ Michel Marcus, Jan 31 2016

(Python)

from sympy import factorint

def A228122(n):

    k = 0

    while sum(factorint(k*(k+1)+41).values()) != n:

        k += 1

    return k # Chai Wah Wu, Sep 07 2018

CROSSREFS

Cf. A005846, A007634, A145292, A145293, A056561.

Sequence in context: A168192 A251129 A007772 * A247408 A285855 A210355

Adjacent sequences:  A228119 A228120 A228121 * A228123 A228124 A228125

KEYWORD

nonn,more

AUTHOR

Shyam Sunder Gupta, Aug 11 2013

EXTENSIONS

a(9) from Zak Seidov, Feb 01 2016

a(10) from Giovanni Resta, Sep 08 2018

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 21 18:13 EDT 2019. Contains 325199 sequences. (Running on oeis4.)