A251240 - OEIS

%I #13 Sep 20 2018 00:30:57

%S 4,5,11,40,124,187,273,313,505,747,751,1280,1478,1563,1841,2386,3130,

%T 3134,4196,4493,4497,5455,6002,6877,8158,9047,9276,10190,10194,11157,

%U 14182,15086,16762,16766,19758,20051,21749,23435,24601,26398,28655,28659,32636

%N Indices of squares of primes in A098550.

%C A098550(a(n)) = A001248(n);

%C A062799(A098550(a(n))) = 2.

%H Chai Wah Wu, <a href="/A251240/b251240.txt">Table of n, a(n) for n = 1..175</a>

%o (Haskell)

%o a251240 n = a251240_list !! (n-1)

%o a251240_list = filter ((== 2) . a062799 . fromIntegral . a098550) [1..]

%o (Python)

%o from gmpy2 import gcd, is_square, is_prime, isqrt

%o A251240_list, l1, l2, s, b = [], 3, 2, 4, {}

%o for n in range(4,10**4):

%o ....i = s

%o ....while True:

%o ........if not i in b and gcd(i,l1) == 1 and gcd(i,l2) > 1:

%o ............l2, l1, b[i] = l1, i, 1

%o ............while s in b:

%o ................b.pop(s)

%o ................s += 1

%o ............if is_square(i) and is_prime(isqrt(i)):

%o ................A251240_list.append(n)

%o ............break

%o ........i += 1 # _Chai Wah Wu_, Dec 06 2014

%Y Cf. A098550, A001248, A062799, subsequence of A251241.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Dec 02 2014