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Search: id:A117477
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| A117477 |
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Primes whose SOD and that of their indices are both prime and equal (indices may not be prime, but their SOD must be prime). |
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+0
2
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| 131, 263, 1039, 1091, 1301, 1361, 1433, 2221, 2441, 2591, 2663, 2719, 2803, 3433, 3631, 4153, 4357, 4397, 5507, 5701, 5741, 5927, 6311, 6353, 6553, 6737, 6827, 6971, 7013, 7213, 7411, 7523, 7741, 8821, 9103, 11173, 11353, 11731, 11821, 12277, 12347
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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"SOD" = "sum of digits".
This sequence is a subset of A033548, the difference being that this sequence requires prime SODs.
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FORMULA
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Find primes whose indices, when SODs are computed, are both prime and SOD(i) = SOD(p)
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EXAMPLE
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a(3) = 1039, the 175th prime. Both the SOD of the index and the prime are prime and equal: 13 = 13.
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PROGRAM
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UBASIC 20 'SOD prime index and SOD prime 30 Y=1 40 Y=nxtprm(Y) 50 C=C+1:print C; Y; "-"; 60 D=str(C):Z=str(Y) 70 E=len(D):F=len(Z) 80 for Q=2 to E 90 A=mid(D, Q, 1):G=val(A) 100 I=I+G:print I; 110 next Q 120 for R=2 to F 130 B=mid(Z, R, 1):H=val(B) 140 J=J+H:print J; 150 next R 160 if I=prmdiv(I) and J=prmdiv(J) and I=J then stop 170 I=0:J=0 180 goto 40
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CROSSREFS
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Cf. A117478, A033548-A033549, A117458-A117463.
Sequence in context: A142616 A132249 A033548 this_sequence A089316 A142129 A068680
Adjacent sequences: A117474 A117475 A117476 this_sequence A117478 A117479 A117480
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KEYWORD
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easy,nonn,base
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AUTHOR
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Enoch Haga (Enokh(AT)comcast.net), Mar 19 2006
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