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 A232450 Largest prime factor of the Belphegor number B(n) = (10^(n+3) + 666)*10^(n+1) + 1. 4
 16661, 1103, 1417831, 1143749, 14282381, 11699423, 1950071, 7503425119, 3837692792387, 145857793, 76607717987, 1755833757671518620617, 17416012536871141, 1000000000000066600000000000001, 16540928199996367, 744657085412168192717253704669 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS The Belphegor numbers (A232449), though not often prime themselves (see A232448), tend to contain very large prime factors and are therefore hard to factorize. LINKS Stanislav Sykora, Table of n, a(n) for n = 0..44 Clifford A. Pickover, Belphegor's Prime: 1000000000000066600000000000001 Wikipedia, Belphegor's prime MATHEMATICA Table[FactorInteger[(10^(n + 3) + 666)*10^(n + 1) + 1][[-1, 1]], {n, 20}] (* T. D. Noe, Nov 25 2013 *) PROG (PARI) default(factor_proven, 1); Belphegor(k)=(10^(k+3)+666)*10^(k+1)+1; LargestPrimeFactor(k)={local(f); f=factor(k); return(f[#f[, 1], 1])}; nmax=40; v=vector(nmax); for (n=0, #v-1, v[n+1]=LargestPrimeFactor(Belphegor(n)); print(v[n+1])) CROSSREFS Cf. A232448 (indices of Belphegor primes), A232449 (Belphegor numbers). Sequence in context: A247693 A170788 A057329 * A317179 A196023 A108843 Adjacent sequences:  A232447 A232448 A232449 * A232451 A232452 A232453 KEYWORD nonn AUTHOR Stanislav Sykora, Nov 24 2013 STATUS approved

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Last modified December 10 12:33 EST 2018. Contains 318047 sequences. (Running on oeis4.)