A176888 Unsafe primes minus 1.
1, 2, 12, 16, 18, 28, 30, 36, 40, 42, 52, 60, 66, 70, 72, 78, 88, 96, 100, 102, 108, 112, 126, 130, 136, 138, 148, 150, 156, 162, 172, 180, 190, 192, 196, 198, 210, 222, 228, 232, 238, 240, 250, 256, 268, 270, 276, 280, 282, 292, 306, 310, 312, 316, 330, 336
Offset: 1
Keywords
Programs
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Mathematica
Select[Prime[Range[70]]-1,PrimeOmega[#]!=2&] (* Harvey P. Dale, Jan 14 2015 *)
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PARI
is(n)=isprime(n+1) && !isprime(n\2) \\ Charles R Greathouse IV, Dec 29 2024
Formula
a(n) = A059456(n) - 1.
a(n) ~ n log n. - Charles R Greathouse IV, Dec 29 2024
Extensions
Entries checked by R. J. Mathar, May 06 2010
Comments