login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A308938
Smallest deficient number which is the product of n consecutive primes.
0
1, 2, 15, 105, 1155, 85085, 1616615, 37182145, 1078282205, 247357937827, 10141675450907, 436092044389001, 20496326086283047, 1086305282573001491, 64092011671807087969, 3909612711980232366109, 261944051702675568529303, 18598027670889965365580513
OFFSET
0,2
COMMENTS
a(n) is greater than A087234(n) for n = 2, 5, 6, 9, 10, 11, 12, 13, 14, 18, ... By definition, A087234(n) is never greater than a(n).
EXAMPLE
a(5) = 5*7*11*13*17 = 85085.
MATHEMATICA
a[n_] := Module[{p = Prime@Range[n]}, While[Times@@(1+1/p) >= 2, p = Rest @ AppendTo[p, NextPrime@p[[-1]]]]; Times@@p]; Array[a, 18, 0] (* Amiram Eldar, Jul 04 2019 *)
PROG
(PARI) a(n)=for(k=1, +oo, p=prod(i=k, k+n-1, prime(i)); sigma(p)<2*p && return(p))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jeppe Stig Nielsen, Jul 01 2019
STATUS
approved