This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A141241 #24 Feb 26 2025 01:59:15 %S A141241 1,4,4,4,6,4,4,6,6,4,4,8,4,4,6,8,6,4,4,4,9,4,4,8,8,6,6,4,10,6,4,6,8,4, %T A141241 8,4,4,12,4,6,4,8,6,4,8,12,4,6,6,4,8,10,4,12,4,4,4,8,12,4,6,4,4,4,12, %U A141241 6,6,9,8,8,8,4,12,8,4,10,8,4,6,6,4,4,16,4,4,6,4,12,8,4,8,12,4,4,8,8,8,12,4 %N A141241 a(n) = number of divisors of n-th positive integer with a nonprime number of divisors. a(n) = the number of divisors of A139118(n). %C A141241 a(1) = 1 and all other terms are composite, of course. %H A141241 John Tyler Rascoe, <a href="/A141241/b141241.txt">Table of n, a(n) for n = 1..10000</a> %F A141241 a(n) = A000005(A139118(n)). - _Michel Marcus_, Feb 26 2025 %t A141241 Select[DivisorSigma[0,Range[200]],!PrimeQ[#]&] (* _Harvey P. Dale_, Mar 20 2015 *) %o A141241 (PARI) for(i=1,200,if(!isprime(numdiv(i)),print1(numdiv(i)","))) \\ _Franklin T. Adams-Watters_, Apr 09 2009 %o A141241 (Python) %o A141241 from sympy import primepi, integer_nthroot, primerange, divisor_count %o A141241 def A141241(n): %o A141241 def f(x): return int(n+sum(primepi(integer_nthroot(x,k-1)[0]) for k in primerange(x.bit_length()+1))) %o A141241 m, k = n, f(n) %o A141241 while m != k: m, k = k, f(k) %o A141241 return divisor_count(m) # _Chai Wah Wu_, Feb 22 2025 %Y A141241 Cf. A000005, A139118, A141242. %K A141241 nonn %O A141241 1,2 %A A141241 _Leroy Quet_, Jun 16 2008 %E A141241 More terms from _Franklin T. Adams-Watters_, Apr 09 2009