A267097 - OEIS

%I #11 Feb 03 2016 17:01:11

%S 0,0,1,1,1,2,3,3,3,4,4,5,6,6,6,7,7,8,8,8,9,9,9,10,11,12,12,12,13,14,

%T 14,14,15,15,16,16,17,17,17,18,18,19,19,20,21,21,21,21,21,22,23,23,24,

%U 24,25,25,26,26,27,28,28,29,29,29,30,31,31,32,32,33,34,34,34,35,35,35,36,37,38,39,39,40,40,41

%N a(n) = number of 4k+1 primes among first n primes; least monotonic left inverse of A080147.

%C a(n) = number of 4k+1 primes (A002144) among primes in range 2 .. A000040(n).

%H Antti Karttunen, <a href="/A267097/b267097.txt">Table of n, a(n) for n = 1..65537</a>

%F Other identities. For all n >= 1:

%F a(A080147(n)) = n.

%F a(n) + A267098(n) = n-1.

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

%o (define A267097 (LEFTINV-LEASTMONO 1 1 A080147))

%Y Cf. A000040, A002144, A080147, A267098.

%Y Cf. also A267101.

%K nonn

%O 1,6

%A _Antti Karttunen_, Feb 01 2016