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A061141 Compute sum of divisors of the prime(n+1)-prime(n)-1 composite numbers between two consecutive primes; choose the largest. 3
7, 12, 18, 28, 31, 39, 42, 60, 72, 91, 90, 96, 84, 124, 120, 168, 144, 144, 195, 168, 186, 224, 252, 217, 216, 210, 280, 248, 360, 255, 336, 288, 403, 372, 392, 378, 294, 480, 372, 546, 384, 508, 399, 468, 576, 600, 504, 560, 450, 546, 744, 504, 728, 588, 720 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

LINKS

Michael S. Branicky, Table of n, a(n) for n = 2..10001 (terms 2..1002 from Harry J. Smith)

FORMULA

a(n) = Max{sigma(c); p(n+1) > c > p(n)}, c is composite, p(n) is the n-th prime and sigma=A000203().

MATHEMATICA

Max[DivisorSigma[1, Range[#[[1]]+1, #[[2]]-1]]]&/@Partition[Prime[ Range[2, 60]], 2, 1] (* Harvey P. Dale, May 19 2017 *)

PROG

(PARI) { n=1; q=3; forprime (p=5, prime(1003), a=0; for (i=q + 1, p - 1, a=max(sigma(i), a)); q=p; write("b061141.txt", n++, " ", a) ) } \\ Harry J. Smith, Jul 18 2009

(Python)

from sympy import prime, divisor_sigma as sigma

def a(n): return max(sigma(c) for c in range(prime(n)+1, prime(n+1)))

print([a(n) for n in range(2, 57)]) # Michael S. Branicky, Jul 12 2021

CROSSREFS

Cf. A000040, A000203, A061120, A335579.

Sequence in context: A022953 A030714 A190036 * A256381 A272975 A190495

Adjacent sequences:  A061138 A061139 A061140 * A061142 A061143 A061144

KEYWORD

nonn

AUTHOR

Labos Elemer, May 29 2001

EXTENSIONS

Offset changed by Michael S. Branicky, Jul 12 2021

STATUS

approved

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Last modified November 27 07:28 EST 2021. Contains 349365 sequences. (Running on oeis4.)