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 A259562 Numbers n such that the sum of the distinct prime factors of prime(n)-1 and prime(n+1)-1 are the same. 1
 2, 414, 556, 3962, 4972, 6151, 6521, 8440, 8665, 13769, 13909, 15576, 16696, 17176, 19926, 20630, 21541, 27090, 30822, 62118, 65349, 74014, 94203, 98600, 101231, 103058, 108333, 112332, 136036, 142714, 145588, 147150, 160730, 162366, 169137, 194681, 200837 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Although there are more terms than A105403 so far, these numbers are still fairly uncommon. Is this sequence infinite? It would follow from the generalized Bunyakovsky conjecture that, e.g., there are infinitely many primes p such that p+2, p+12, p+14, 6*p^2+84*p+1 and 6*p^2+84*p+145 are all prime, and there are no primes between 6*p^2+84*p+1 and 6*p^2+84*p+145. If so, then the sequence is infinite, because it contains n where prime(n) = 6*p^2+84*p+1, with prime(n)-1 having distinct prime factors 2,3,p,p+14 and prime(n+1) having distinct prime factors 2,3,p+2,p+12. - Robert Israel, Jun 30 2015 LINKS EXAMPLE The prime factors of prime(414)-1 are 2,3,5,5,19 and the prime factors of prime(415)-1 are 2,2,2,3,7,17. The sum of the distinct entries in each of these lists is 29. MAPLE Primes:= select(isprime, [2, seq(2*i+1, i=1..10^6)]): spf:= map(p -> convert(numtheory:-factorset(p-1), `+`), Primes): select(t -> spf[t+1]=spf[t], [\$1..nops(Primes)-1]); MATHEMATICA Select[Range@ 250000, Total[First /@ FactorInteger[Prime@ # - 1]] == Total[First /@ FactorInteger[Prime[# + 1] - 1]] &] (* Michael De Vlieger, Jul 01 2015 *) PROG (PARI) spf(n) = {my(f=factor(n)); sum(k=1, #f~, f[k, 1]); } lista(nn) = {forprime(p=2, nn, if (spf(p-1)==spf(nextprime(p+1)-1), print1(primepi(p), ", ")); ); } \\ Michel Marcus, Jun 30 2015 CROSSREFS Cf. A008472, A105403, A259564. Sequence in context: A067827 A070269 A153911 * A177321 A080392 A154541 Adjacent sequences:  A259559 A259560 A259561 * A259563 A259564 A259565 KEYWORD nonn AUTHOR Otis Tweneboah, Pratik Koirala, Eugene Fiorini, Nathan Fox, Jun 30 2015 EXTENSIONS More terms from Alois P. Heinz, Jun 30 2015 STATUS approved

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Last modified October 26 14:28 EDT 2021. Contains 348267 sequences. (Running on oeis4.)