This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A341669 #13 Mar 04 2021 01:42:28 %S A341669 863,1439,2039,3167,3803,4799,10559,11423,14087,14207,15287,15803, %T A341669 16139,18743,20663,21059,21179,22343,25307,25919,26459,29483,29759, %U A341669 30803,32507,32987,33107,34319,34367,35879,43427,45887,46559,46643,46919,54959,57119,57587 %N A341669 Primes p such that p^7 - 1 has 8 divisors. %C A341669 For each term p, p^7 - 1 = (p-1)*(p^6 + p^5 + p^4 + p^3 + p^2 + p + 1) is a number of the form 2*q*r (where q and r are distinct primes): p-1 = 2*q and p^6 + p^5 + p^4 + p^3 + p^2 + p + 1 = r. %C A341669 Conjecture: sequence is infinite. %e A341669 p = %e A341669 n a(n) factorization of p^7 - 1 %e A341669 - ----- ------------------------------------ %e A341669 1 863 2 * 431 * 413588356833933793 %e A341669 2 1439 2 * 719 * 8885189025331426081 %e A341669 3 2039 2 * 1019 * 71897932302115976281 %e A341669 4 3167 2 * 1583 * 1009312223899992366817 %e A341669 5 3803 2 * 1901 * 3026022586778671180093 %e A341669 6 4799 2 * 2399 * 12217856103420111345601 %e A341669 7 10559 2 * 5279 * 1386046726502834819142721 %e A341669 8 11423 2 * 5711 * 2221872233870122705845793 %e A341669 9 14087 2 * 7043 * 7815232779386331437540137 %t A341669 Select[Range[60000], PrimeQ[#] && DivisorSigma[0, #^7 - 1] == 8 &] (* _Amiram Eldar_, Feb 27 2021 *) %o A341669 (PARI) isok(p) = isprime(p) && (numdiv(p^7-1) == 8); \\ _Michel Marcus_, Feb 27 2021 %Y A341669 Cf. A000005, A000040, A309906, A341668. %K A341669 nonn %O A341669 1,1 %A A341669 _Jon E. Schoenfield_, Feb 26 2021