A249893 - OEIS

%I #26 Apr 18 2022 09:47:05

%S 2,25,256,256036,2560361612769,256036161276932002260000001,

%T 256036161276932002260000001607597862784080913990785121

%N a(n+1) is next smallest square not divisible by 10 beginning with a(n), initial term is 2.

%C a(12) has 1717 digits. - _Michael S. Branicky_, Feb 25 2021

%H Michael S. Branicky, <a href="/A249893/b249893.txt">Table of n, a(n) for n = 1..11</a> (terms 1..10 from Hiroaki Yamanouchi)

%o (PARI) a(n)=k=n;s=1;while(s<5*10^7,if(s%10,if(s^2\(10^(#Str(s^2)-#Str(k)))==k,print1(s^2,", ");k=s^2));s++)

%o a(2)

%o (Python)

%o def f(x):

%o ..print(x,end=', ')

%o ..n = x

%o ..s = 1

%o ..while s < 10**7:

%o ....if s % 10:

%o ......S = str(s**2)

%o ......if S.startswith(str(n)):

%o ........print(s**2,end=', ')

%o ........n = s**2

%o ....s += 1

%o f(2)

%o (Python)

%o from math import isqrt

%o def anext(an):

%o   lo, hi = an*10, an*10 + 9

%o   while True:

%o     found = False

%o     if isqrt(hi)**2 > lo: return (isqrt(lo)+1)**2

%o     lo, hi = lo*10, hi*10 + 9

%o n, an = 1, 2

%o for n in range(2, 17):

%o   an = anext(an)

%o   print(n, an) # _Michael S. Branicky_, Feb 25 2021

%Y Cf. A048559, A048561.

%K nonn,base

%O 1,1

%A _Derek Orr_, Nov 08 2014