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 A070801 Largest prime <= sigma(n): a(n) = prevprime(sigma(n)), where prevprime(n) = A007917(n), the largest prime less than or equal to n. 10
 3, 3, 7, 5, 11, 7, 13, 13, 17, 11, 23, 13, 23, 23, 31, 17, 37, 19, 41, 31, 31, 23, 59, 31, 41, 37, 53, 29, 71, 31, 61, 47, 53, 47, 89, 37, 59, 53, 89, 41, 89, 43, 83, 73, 71, 47, 113, 53, 89, 71, 97, 53, 113, 71, 113, 79, 89, 59, 167, 61, 89, 103, 127, 83, 139, 67, 113, 89 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS Largest integer k such that A000203(k) <= A000203(n)+1. - Antti Karttunen, Nov 07 2017, after Benoit Cloitre's Mar 17 2002 comment in A007917. LINKS Antti Karttunen, Table of n, a(n) for n = 2..16385 FORMULA a(n) = A000040(A000720(sigma(n))) = A007917(A000203(n)). From Reinhard Zumkeller, Jun 26 2003: (Start) A085379(n) <= a(n). a(A085380(n)) = A085379(A085380(n)). a(A085381(n)) > A085379(A085381(n)). a(A023194(n)) = A000203(A023194(n)). (End) EXAMPLE For n=100: sigma(100) = 217, prevprime(217) = 211 = a(100). MATHEMATICA Table[Prime[PrimePi[DivisorSigma[1, w]]], {w, 2, 128}] PROG (PARI) A070801(n) = precprime(sigma(n)); \\ Antti Karttunen, Nov 07 2017 (Scheme) (define (A070801 n) (let ((s1 (+ 1 (A000203 n)))) (let loop ((k s1)) (if (<= (A000203 k) s1) k (loop (- k 1)))))) ;; (For code of A000203, see under that entry). Antti Karttunen, Nov 07 2017 CROSSREFS Cf. A000203, A007917, A070800, A000040, A000720, A023194, A085379, A085380, A085381, A202111. Sequence in context: A245550 A318461 A085379 * A114753 A079316 A106481 Adjacent sequences:  A070798 A070799 A070800 * A070802 A070803 A070804 KEYWORD easy,nonn AUTHOR Labos Elemer, May 08 2002 STATUS approved

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Last modified July 25 16:03 EDT 2021. Contains 346291 sequences. (Running on oeis4.)