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A190052 Least number having exactly two odd prime factors that differ by 2*n^2. 3

%I

%S 15,33,115,185,159,553,303,393,835,2321,7859,1465,3839,1985,3199,5753,

%T 13823,3265,3635,8921,4435,2913,3183,12793,37091,40049,19123,4713,

%U 18623,19921,21263,10265,64003,67889,41939,44353,8223,84593,21343,9609,37103,17665

%N Least number having exactly two odd prime factors that differ by 2*n^2.

%H Nathaniel Johnston, <a href="/A190052/b190052.txt">Table of n, a(n) for n = 1..10000</a>

%e a(11) = 7859 because 7859 = 29 * 271, and 271 - 29 = 242 = 2*11^2.

%p A190052 := proc(n) local k,p: k:=1: do p:=ithprime(k): if(isprime(p+2*n^2))then return p*(p+2*n^2): fi: k:=k+1: od: end: seq(A190052(n),n=1..50); # _Nathaniel Johnston_, May 04 2011

%t f[n_] := Block[{p = 3}, While[q=p+2*n^2; ! PrimeQ[q], p=NextPrime[p]]; p*q]; Table[ f[n], {n, 60}]

%K nonn,easy

%O 1,1

%A _Michel Lagneau_, May 04 2011

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Last modified October 18 23:08 EDT 2019. Contains 328211 sequences. (Running on oeis4.)