

A258883


Primitive weird numbers (PWN) of the form 2^k*p*q*r with k > 0 and where p < q < r are odd primes.


13



4030, 5830, 45356, 91388, 243892, 254012, 338572, 343876, 388076, 1713592, 8812312, 9928792, 11339816, 11547352, 15126992, 17999992, 29581424, 38546576, 74899952, 85389368, 89283592, 95327216, 141659096, 146764264, 162079768, 173482552, 569494624, 632874016
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OFFSET

1,1


COMMENTS

The condition k > 0 is not really a limitation since a product of three odd primes cannot be weird.  Numbers of the form 2^k*p^2*q having only two distinct odd prime divisors, e.g., A258401(45) = 2319548096 = 2^6 * 137^2 * 1931 or A258401(143) = 232374697216 = 2^8 * 797^2 * 1429, are neither in A258882 nor in the present sequence as it is currently defined, although they are in the set of weird numbers 2^k*p*q*r with odd primes p,q,r. (PWN with nonsquarefree odd part are listed in A273815.)  M. F. Hasler, Jul 18 2016, amended Nov 09 2017
It appears that there are (2, 7, 12, 18, 41, ...) terms with k = valuation(a(n),2) = 1, 2, 3, etc. The smallest and largest such are (4030, 45356, 1713592, 15126992, 569494624, 5353519168, 96743686016, 1009572479744, ...) resp. (5830, 388076, 173482552, 6587973136, 297512429728, ...).  M. F. Hasler, Nov 09 2017


LINKS

M. F. Hasler, Table of n, a(n) for n = 1..121 (Using A002975(1..1073) calculated by Robert G. Wilson v.)


EXAMPLE

a(1) = 4030 = 2*5*13*31.
a(2) = 5830 = 2*5*11*53.
a(3) = 45356 = 2^2*17*23*29.


MATHEMATICA

(* copy the terms from A002975, assign them to 'lst' and then *) Select[ lst, PrimeNu@# == 4 &] (* WARNING: this code selects PWN with 3 distinct odd prime factors but does not exclude that they occur with multiplicity > 1, which is forbidden by definition of this sequence.  M. F. Hasler, Jul 12 2016 *)


PROG

(PARI) select(w>factor(w)[, 2][^1]~==[1, 1, 1], A002975) \\ Assuming that A002975 is defined as set or vector.  M. F. Hasler, Jul 12 2016


CROSSREFS

Cf. A002975, A258401, A258882, A258884, A258885.
Sequence in context: A242864 A247689 A258401 * A249107 A234838 A234834
Adjacent sequences: A258880 A258881 A258882 * A258884 A258885 A258886


KEYWORD

nonn


AUTHOR

Douglas E. Iannucci and Robert G. Wilson v, Jun 14 2015


STATUS

approved



