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 A234693 Primes of the form n^2 + 1 such that (n - 1)^2 + 1 and (n + 1)^2 + 1 are semiprimes. 1
 17, 101, 28901, 324901, 608401, 902501, 2016401, 5664401, 7452901, 14822501, 16974401, 18490001, 34222501, 40449601, 41731601, 46240001, 48580901, 50410001, 52417601, 76038401, 92736901, 103022501, 111936401, 121220101, 124768901, 139948901, 151290001 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The corresponding n are 4, 10, 170, 570, 780, 950, 1420, 2380... Property: n^2 + 1 = p + q - 1 and for a(n) > 17, a(n) == 1 mod 100. LINKS Donovan Johnson and Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (first 1000 terms from Johnson) EXAMPLE 101 = 10^2 + 1 is in the sequence because 9^2 + 1 = 2*41 and 11^2 + 1 = 2*61. MAPLE with(numtheory):for n from 1 to 10^5 do:n1:=n^2+1:n2:=(n+1)^2+1:n3:=(n+2)^2+1: if type(n2, prime)=true and bigomega(n1)=2 and bigomega(n3)=2 then printf(`%d, `, n2):else fi:od: PROG (PARI) forstep(n=4, 1e5, 2, if(isprime(n^2+1) && isprime(n^2/2-n+1) && isprime(n^2/2+n+1), print1(n^2+1", "))) \\ Charles R Greathouse IV, Dec 29 2013 CROSSREFS Cf. A002496, A144255, A085722. Sequence in context: A215234 A145943 A331950 * A022677 A275919 A229425 Adjacent sequences:  A234690 A234691 A234692 * A234694 A234695 A234696 KEYWORD nonn AUTHOR Michel Lagneau, Dec 29 2013 STATUS approved

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Last modified July 29 01:22 EDT 2021. Contains 346340 sequences. (Running on oeis4.)