A105408 - OEIS

A105408

Indices n of primes p(n), p(n+4) such that p(n)+1 and p(n+4)+1 have the same largest prime factor.

1, 3, 5, 16, 64, 85, 266, 547, 1709, 1771, 4415, 9545, 13129, 24130, 34201, 213122, 396981, 543586, 555301, 609182, 1040051, 1870869, 2547634, 3052012, 5076662, 8530768, 9773479, 18563382, 26505870, 89046072, 169660944, 193691856, 200228233, 359241899, 597825925, 914450195, 1020520062, 1585841242, 1970793485

(list; graph; refs; listen; history; text; internal format)

OFFSET

2,2

LINKS

Table of n, a(n) for n=2..40.

EXAMPLE

p(1)+1=3 and p(5)+1=12 have the same largest prime factor.

PROG

(PARI) \prime indices such that gd of prime(x)+ k and prime(x+m) + k are equal divpm1(n, m, k) = { local(x, l1, l2, v1, v2); for(x=2, n, v1 = ifactor(prime(x)+ k); v2 = ifactor(prime(x+m)+k); l1 = length(v1); l2 = length(v2); if(v1[l1] == v2[l2], print1(x", ") ) ) } ifactor(n) = \Vector of the prime factors of n { local(f, j, k, flist); flist=[]; f=Vec(factor(n)); for(j=1, length(f[1]), for(k = 1, f[2][j], flist = concat(flist, f[1][j]) ); ); return(flist) }

CROSSREFS

Sequence in context: A208819 A038120 A192911 * A291963 A375911 A242104

Adjacent sequences: A105405 A105406 A105407 * A105409 A105410 A105411

KEYWORD

nonn

AUTHOR

Cino Hilliard, May 01 2005

EXTENSIONS

More terms from Erich Friedman, Aug 26 2005

Corrected and extended by Donovan Johnson, Apr 03 2008

STATUS

approved