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A247820
Numbers k such that sigma(2*k-1) is a prime p.
11
5, 13, 145, 365, 841, 1201, 1741, 2521, 3961, 5101, 7813, 8581, 13945, 14281, 14965, 41761, 42925, 73345, 139921, 229165, 245701, 265721, 276025, 289561, 298765, 341965, 351961, 353641, 367225, 414961, 595141, 601705, 676285, 697381, 711625, 740545, 942565
OFFSET
1,1
COMMENTS
Supersequence of A247789.
Corresponding values of primes p for a(n) are A008438(a(n)-1) or A247837.
LINKS
Martin Møller Skarbiniks Pedersen, Table of n, a(n) for n = 1..1000
EXAMPLE
Number 13 is in sequence because sigma(2*13-1) = sigma(25) = 31 (prime).
PROG
(Magma) [n: n in [1..10000000] | IsPrime(SumOfDivisors(2*n-1))];
(PARI) for(n=1, 10^7, if(isprime(sigma(2*n-1)), print1(n, ", "))) \\ Derek Orr, Sep 25 2014
CROSSREFS
KEYWORD
nonn,changed
AUTHOR
Jaroslav Krizek, Sep 24 2014
STATUS
approved