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A067891 Primes p such that sigma(p+1) = sigma(p-1). 5
367, 919, 30593, 95393, 117571, 124759, 147341, 197261, 334541, 344417, 463219, 732257, 755081, 931757, 982759, 1996759, 2401219, 2962697, 3013447, 4722941, 7892827, 13333097, 13358407, 17946259, 19828483, 19855471, 19904981 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..769 (terms < 10^12)

MATHEMATICA

fQ[p_] := DivisorSigma[1, p - 1] == DivisorSigma[1, p + 1]; p = 2; lst = {}; While[p < 100000000, If[fQ@ p, AppendTo[lst, p]]; p = NextPrime@ p]; lst (* Vladimir Joseph Stephan Orlovsky, Dec 03 2009 and modified by Robert G. Wilson v, May 08 2016 *)

PROG

(PARI) for(n=2, 10^8, if(isprime(n) && sigma(n+1)==sigma(n-1), print1(n, ", "))) \\ It is more efficient to use forprime(...).

(PARI) is_A067891(p)=sigma(p-1)==sigma(p+1)&&isprime(p) \\ M. F. Hasler, Jul 31 2015

CROSSREFS

Cf. A067889 (analog with tau).

Sequence in context: A060518 A065556 A068357 * A142579 A307010 A098823

Adjacent sequences:  A067888 A067889 A067890 * A067892 A067893 A067894

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Mar 02 2002

EXTENSIONS

More terms from Rick L. Shepherd, Apr 19 2002

STATUS

approved

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Last modified May 27 03:41 EDT 2020. Contains 334647 sequences. (Running on oeis4.)