A087454 Multiplicative inverse of the n-th prime prime(n) modulo prime(n-1).
1, 2, 3, 2, 6, 10, 9, 5, 4, 15, 26, 28, 21, 11, 8, 9, 30, 51, 17, 36, 61, 20, 14, 78, 73, 51, 26, 54, 82, 105, 32, 22, 69, 14, 75, 126, 131, 41, 28, 29, 90, 163, 96, 145, 99, 83, 88, 56, 114, 172, 39, 120, 217, 42, 43, 44, 135, 226, 208, 141, 85, 21, 77, 156, 235, 68, 276
Offset: 2
Examples
We have a(7) = 10 because prime(7)*10 = 170 = 1 [mod 13] = 1 [mod prime(6)].
Links
- Charles R Greathouse IV, Table of n, a(n) for n = 2..10000
Programs
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Magma
[InverseMod(NthPrime(n), NthPrime(n-1)): n in [2..70]]; // G. C. Greubel, Aug 09 2019
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Maple
seq(`mod`(1/ithprime(n), ithprime(n-1)), n = 2..70); # G. C. Greubel, Aug 09 2019
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Mathematica
Table[PowerMod[Prime[n], -1, Prime[n - 1]], {n, 2, 68}] (* Geoffrey Critzer, May 16 2015 *) -
PARI
a(n)=my(p=prime(n-1),g=nextprime(p+1)-p);lift(Mod(1/g,p)) \\ Charles R Greathouse IV, Aug 23 2011
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Sage
[nth_prime(n).inverse_mod(nth_prime(n-1)) for n in (2..70)] # G. C. Greubel, Aug 09 2019
Extensions
Corrected and extended by Ray Chandler, Oct 24 2003