cp's OEIS Frontend

A246261 Numbers n such that A003961(n) is of the form 4k+1.

%I A246261 #18 Mar 12 2021 15:56:46
%S A246261 1,3,4,9,10,11,12,13,14,16,23,25,27,30,31,33,34,35,36,37,38,39,40,42,
%T A246261 44,47,48,49,52,56,58,59,64,69,71,75,81,82,83,85,86,89,90,92,93,95,97,
%U A246261 99,100,102,105,106,107,108,109,110,111,114,117,119,120,121,122,124,126,130,131,132,133,134,136,139,140,141,143,144
%N A246261 Numbers n such that A003961(n) is of the form 4k+1.
%C A246261 Equally: numbers n for which A048673(n) is odd.
%C A246261 Also, after 1, numbers n for which A243062(n) is even.
%H A246261 Antti Karttunen, <a href="/A246261/b246261.txt">Table of n, a(n) for n = 1..10001</a>
%F A246261 For all n >= 1, A246262(a(n)) = n.
%t A246261 {1}~Join~Select[Range[144], Mod[Times @@ Map[NextPrime[#1]^#2 & @@ # &, FactorInteger[#]], 4] == 1 &] (* _Michael De Vlieger_, Mar 12 2021 *)
%o A246261 (Scheme, with _Antti Karttunen_'s IntSeq-library)
%o A246261 (define A246261 (MATCHING-POS 1 1 (lambda (n) (= 1 (modulo (A003961 n) 4)))))
%o A246261 (Python)
%o A246261 from sympy import factorint, prime, primepi
%o A246261 from operator import mul
%o A246261 def a003961(n):
%o A246261     f=factorint(n)
%o A246261     return 1 if n==1 else reduce(mul, [prime(primepi(i) + 1)**f[i] for i in f])
%o A246261 print([n for n in range(1, 201) if a003961(n)%4==1]) # _Indranil Ghosh_, Jun 12 2017
%Y A246261 Complement: A246263.
%Y A246261 Positions of zeros in A246271.
%Y A246261 Inverse function: A246262.
%Y A246261 The first row of array A246259.
%Y A246261 Cf. A003961, A048673, A243062, A246265.
%K A246261 nonn
%O A246261 1,2
%A A246261 _Antti Karttunen_, Aug 21 2014