A177942 Smallest prime divisor of (A177941(n))^2-4.

3, 3, 7, 13, 5, 3, 5, 3, 37, 7, 79, 7, 163, 5, 3, 5, 3, 11, 3, 349, 17, 3, 5, 3, 5, 3, 17, 3, 5, 3, 5, 3, 757, 17, 3, 5, 3, 23, 3, 5, 3, 1567, 13, 5, 3, 5, 3, 7, 3163, 5, 3, 5, 3, 17, 3, 5, 3, 5, 3, 23, 3, 5, 3, 37, 7, 17, 3, 7, 23, 3, 13, 7, 5, 3, 5, 3, 7, 11, 3, 5, 3, 5, 3, 6547, 7, 13099, 7, 73

Offset

1,1

Comments

Records are in A177945, indices of records in A177943.

Links

Table of n, a(n) for n=1..88.

Formula

a(n) = A020639((A177941(n))^2-4) .

Mathematica

Differences[NestList[# + FactorInteger[#^2 - 4][[1, 1]] - 1 &, 5, 100]] + 1 (* Amiram Eldar, Dec 14 2018 after Michael De Vlieger at A177941 *)

Prog

(PARI) listap(nn) = {my(va = vector(nn), p); va[1] = 5; for (n=2, nn, p = factor(va[n-1]^2-4)[1, 1]; print1(p, ", "); va[n] = va[n-1] + p - 1; ); } \\ Michel Marcus, Dec 14 2018

Crossrefs

Cf. A177941, A023200, A177930, A177929.

Sequence in context: A126698 A219211 A088859 * A360873 A116880 A051123

Adjacent sequences: A177939 A177940 A177941 * A177943 A177944 A177945

Keyword

nonn

Author

Vladimir Shevelev, May 15 2010

Extensions

Entries checked by R. J. Mathar, Jun 30 2010

Status

approved