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 A063487 #8 Feb 16 2025 08:32:45 %S A063487 0,1,2,3,4,5,7,9,11,13,16,20,25 %N A063487 Number of distinct prime divisors of 2^(2^n)-1 (A051179). %C A063487 2^(2^n)-1 is the product of the first n Fermat numbers F(0),...,F(n-1) (A000215). Hence this sequence is just the summation of A046052, which gives the number of prime factors in each Fermat number. - _T. D. Noe_, Jan 07 2003 %D A063487 D. M. Burton, Elementary Number Theory, Allyn and Bacon Inc., Boston MA, 1976, p. 238. %H A063487 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FermatNumber.html">Fermat Number</a> %o A063487 (PARI) for(n=0,22,print(omega(2^(2^n)-1))) %Y A063487 Cf. A051179, A000215, A046052. %K A063487 nonn %O A063487 0,3 %A A063487 _Jason Earls_, Jul 28 2001 %E A063487 More terms from _T. D. Noe_, Jan 07 2003