%I #18 Mar 12 2021 15:56:46

%S 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 44,47,48,49,52,56,58,59,64,69,71,75,81,82,83,85,86,89,90,92,93,95,97,

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

%C Equally: numbers n for which A048673(n) is odd.

%C Also, after 1, numbers n for which A243062(n) is even.

%H Antti Karttunen, <a href="/A246261/b246261.txt">Table of n, a(n) for n = 1..10001</a>

%F For all n >= 1, A246262(a(n)) = n.

%t {1}~Join~Select[Range[144], Mod[Times @@ Map[NextPrime[#1]^#2 & @@ # &, FactorInteger[#]], 4] == 1 &] (* _Michael De Vlieger_, Mar 12 2021 *)

%o (Scheme, with _Antti Karttunen_'s IntSeq-library)

%o (define A246261 (MATCHING-POS 1 1 (lambda (n) (= 1 (modulo (A003961 n) 4)))))

%o (Python)

%o from sympy import factorint, prime, primepi

%o from operator import mul

%o def a003961(n):

%o f=factorint(n)

%o return 1 if n==1 else reduce(mul, [prime(primepi(i) + 1)**f[i] for i in f])

%o print([n for n in range(1, 201) if a003961(n)%4==1]) # _Indranil Ghosh_, Jun 12 2017

%Y Complement: A246263.

%Y Positions of zeros in A246271.

%Y Inverse function: A246262.

%Y The first row of array A246259.

%Y Cf. A003961, A048673, A243062, A246265.

%K nonn

%O 1,2

%A _Antti Karttunen_, Aug 21 2014