A177930 - OEIS

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A177930

a(n) is the smallest prime divisor of (A177929(n)-1)*(A177929(n)+1).

3, 5, 3, 11, 3, 5, 3, 29, 3, 59, 3, 7, 5, 3, 7, 137, 3, 5, 3, 281, 3, 5, 3, 569, 3, 7, 5, 3, 1151, 3, 5, 3, 2309, 3, 31, 4649, 3, 17, 3, 7, 5, 3, 7, 5, 3, 9341, 3, 5, 3, 11, 3, 59, 3, 29, 3, 19, 7, 5, 3, 7, 19, 5, 3, 7, 109, 5, 3, 61, 7, 79, 5, 3, 13, 5, 3, 19139, 3, 101, 3, 7, 13, 11, 3, 71, 3

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OFFSET

1,1

COMMENTS

Records are in A177932, their positions in A177931.

LINKS

Table of n, a(n) for n=1..85.

FORMULA

a(n) = A020639( (A177929(n))^2 -1 ).

MATHEMATICA

lpf[n_] := FactorInteger[n][[1, 1]];

b[n_] := b[n] = If[n == 1, 4, b[n-1]+lpf[b[n-1]^2-1]-1];