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 A070689 Numbers k such that k+1 and k^2+1 are primes. 18
 1, 2, 4, 6, 10, 16, 36, 40, 66, 126, 130, 150, 156, 180, 210, 240, 250, 256, 270, 280, 306, 396, 400, 420, 430, 466, 490, 556, 570, 576, 646, 690, 700, 750, 760, 826, 906, 910, 936, 946, 966, 1060, 1096, 1150, 1276, 1290, 1306, 1320, 1366, 1566, 1570 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For any n > 1 in this sequence, (n+1)*(n^2+1) has the same nonzero digits as its prime factors in base n. - Ely Golden, Dec 12 2016 LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Zak Seidov) MATHEMATICA Select[ Range[2000], PrimeQ[ # + 1] && PrimeQ[ #^2 + 1] & ] PROG (PARI) list(lim)=my(v=List()); forprime(p=2, lim+1, if(isprime(1+(p-1)^2), listput(v, p-1))); Vec(v) \\ Charles R Greathouse IV, Dec 13 2016 CROSSREFS Cf. A067720. Sequence in context: A164142 A048833 A204656 * A339312 A091611 A107742 Adjacent sequences:  A070686 A070687 A070688 * A070690 A070691 A070692 KEYWORD nonn AUTHOR Robert G. Wilson v, May 13 2002 STATUS approved

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Last modified December 6 22:42 EST 2021. Contains 349567 sequences. (Running on oeis4.)