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A251240 Indices of squares of primes in A098550.

%I A251240 #19 Jan 26 2025 09:10:46
%S A251240 4,5,11,40,124,187,273,313,505,747,751,1280,1478,1563,1841,2386,3130,
%T A251240 3134,4196,4493,4497,5455,6002,6877,8158,9047,9276,10190,10194,11157,
%U A251240 14182,15086,16762,16766,19758,20051,21749,23435,24601,26398,28655,28659,32636
%N A251240 Indices of squares of primes in A098550.
%H A251240 Chai Wah Wu, <a href="/A251240/b251240.txt">Table of n, a(n) for n = 1..175</a>
%F A251240 A098550(a(n)) = A001248(n).
%F A251240 A062799(A098550(a(n))) = 2.
%o A251240 (Haskell)
%o A251240 a251240 n = a251240_list !! (n-1)
%o A251240 a251240_list = filter ((== 2) . a062799 . fromIntegral . a098550) [1..]
%o A251240 (Python)
%o A251240 from gmpy2 import gcd, is_square, is_prime, isqrt
%o A251240 A251240_list, l1, l2, s, b = [], 3, 2, 4, {}
%o A251240 for n in range(4,10**4):
%o A251240     i = s
%o A251240     while True:
%o A251240         if not i in b and gcd(i,l1) == 1 and gcd(i,l2) > 1:
%o A251240             l2, l1, b[i] = l1, i, 1
%o A251240             while s in b:
%o A251240                 b.pop(s)
%o A251240                 s += 1
%o A251240             if is_square(i) and is_prime(isqrt(i)):
%o A251240                 A251240_list.append(n)
%o A251240             break
%o A251240         i += 1
%o A251240 print(A251240_list) # _Chai Wah Wu_, Dec 06 2014
%Y A251240 Subsequence of A251241.
%Y A251240 Cf. A001248, A062799, A098550.
%K A251240 nonn
%O A251240 1,1
%A A251240 _Reinhard Zumkeller_, Dec 02 2014