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A259980 Numbers that are 1+prime and have 4 proper divisors. 1
12, 18, 20, 32, 44, 68, 98, 164, 212, 242, 284, 332, 338, 524, 548, 578, 692, 788, 908, 1052, 1124, 1172, 1532, 1724, 1868, 2012, 2084, 2252, 2348, 2372, 2468, 2708, 2732, 2804, 2972, 3188, 3308, 3362, 3548, 3644, 3698, 3908, 3932, 4052, 4244, 4364, 4604, 4652 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Lars Blomberg, Table of n, a(n) for n = 1..10000

R. P. Boas & N. J. A. Sloane, Correspondence, 1974

EXAMPLE

12 is 1+11, and has the proper divisors 2, 3, 4, 6.

MATHEMATICA

Select[Prime@ Range@ 630 + 1, DivisorSigma[0, #] == 6 &] (* Michael De Vlieger, Jul 13 2015 *)

PROG

(PARI)  main(size)={my(v=vector(size), i, t); t=1; for(i=1, size, until(length(divisors(prime(t)+1))-2==4, t++); v[i]=prime(t)+1; t++); return(v); } /* Anders Hellström, Jul 13 2015 */

CROSSREFS

Cf. A008864.

Sequence in context: A098770 A181487 A091191 * A257719 A192819 A071927

Adjacent sequences:  A259977 A259978 A259979 * A259981 A259982 A259983

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Jul 12 2015, following a suggestion from R. P. Boas, May 19 1974

EXTENSIONS

More terms from Lars Blomberg, Jul 13 2015

STATUS

approved

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Last modified September 18 11:42 EDT 2018. Contains 315130 sequences. (Running on oeis4.)