A355237 - OEIS

%I #15 Sep 09 2022 08:04:58

%S 17,8,2,13,20,74,90,137,377,3050,986,1669,4181,6530,1493,8434,9704,

%T 22160,10709,5165,16109,154708,58418,31657,52393,401480,176810,101349,

%U 105572,678356,241882,501716,393817,284002,685541,1437353,1751296,3225578,3439258,2479594

%N First occurrence of difference n between two consecutive terms of A000404. a(n) gives the lower term. The upper term is A355238.

%F a(n) = A355238(n) - n.

%o (Python)

%o from itertools import count

%o from sympy import factorint

%o def A355237(n):

%o     m = 2

%o     for k in count(2):

%o         c = False

%o         for p in (f:=factorint(k)):

%o             if (q:= p & 3)==3 and f[p]&1:

%o                 break

%o             elif q == 1:

%o                 c = True

%o         else:

%o             if c or f.get(2,0)&1:

%o                 if k-m == n:

%o                     return m

%o                 m = k # _Chai Wah Wu_, Jul 01 2022

%Y Cf. A000404, A104271, A355238.

%K nonn

%O 1,1

%A _Hugo Pfoertner_, Jun 30 2022